W DE G
CONTENTS
L i s t of P a r t i c i p a n t s X I I I
SECTION I . ORGANIZATION: BIOCHEMICAL METHODS
I n t r o d u c t i o n : The Biochemistry of Light-Harvesting Complexes by R.J. Cogdell 1
Phycobilisome-Thylakoid I n t e r a c t i o n : The Nature of High Molecular Weight Polypeptides by E. Gantt C.A. L i p s c h u l t z and F.X. Cunningham Jr 11
On the S t r u c t u r e of Photosystem II-Phycobilisome Complexes of Cyanobacteria by E. Mörschel and G.-H. Schatz 21
Stru c t u r e of Cryptophyte Photosynthetic Membranes by W. Wehrmeyer 35
S t r u c t u r a l and Phylogenetic Relationships of Phycoerythrins from Cyanobacteria, Red Algae and Cryptophyceae by W. S i d l e r and H. Zuber 49
I s o l a t i o n and C h a r a c t e r i z a t i o n of the Components of the Phycobilisome from Mastigocladus laminosus and Cross- l i n k i n g Experiments by R. Rümbeli and H. Zuber 61
C-Phycocyanin from Mastigocladus laminosus: Chromophore Assignment i n Higher Aggregates by Cystein M o d i f i c a t i o n by R. Fischer, S. Siebzehnrlibl and H. Scheer 71
Photochromic Prope r t i e s of C-Phycocyanin by G. Schmidt, S. Siebzehnrübl, R. Fischer and H. Scheer 77
Concerning the Relat i o n s h i p of L i g h t Harvesting B i l i - p r o t e i n s t o Phycochromes i n Cyanobacteria by W. Kufer 89
Subunit S t r u c t u r e and Reassembly of the Light-Harvesting Complex from Rhodospiri Hum rubrum G9+ by R. Ghosh, ThT~Rosatzin ancTR. Baclofen 93
Primary S t r u c t u r e Analyses of B a c t e r i a l Antenna Polypeptides - C o r r e l a t i o n of Aromatic Amino Acids w i t h Spectral Properties - S t r u c t u r a l S i m i l a r i t i e s w i t h Reaction Center Polypeptides by R.A. Brunisholz and H. Zuber 103
VIII
The S t r u c t u r e o f the "Core1* of the Purple B a c t e r i a l Photo­ s y n t h e t i c Unit by D.J. Dawkins, L.A. Ferguson and R.J. Cogdell 115
A Comparison o f the Ba c t e r i o c h l o r o p h y l 1 C--Binding Proteins of Chlorobium and Chloroflexus by P.D. Gerola, P. Hpjrup and J.M. Olson 129
I n t e r a c t i o n s between B a c t e r i o c h l o r o p h y l 1 c Molecules i n Oligomers and i n Chlorosomes of Green Photosynthetic Bacteria by D.C. Brune, G.H. King and R.E. Blankenship 141
Ligh t - H a r v e s t i n g Complexes of Chlorophyll c-Containing Algae by A.W.D. Larkum and R.G. H i l l e r 153
I s o l a t i o n and C h a r a c t e r i z a t i o n of a Chloro p h y l l a/c-Hetero- xanthin/Diadinoxanthin Light-Harvesting Complex from P l e u r o c h l o r i s meiringensis (Xanthophyceae) by C. Wilhelm, C. Bliche I and B. Rousseau 167
The Antenna Components of Photosystem I I w i t h Emphasis on the Major Pigment-Protein, LHC l i b by G.F. Peter and P. Thornber 175
SECTION I I : ORGANIZATION: MOLECULAR GENETICS AND CRYSTALLOGRAPHY
Molecular Biology of Antennas by G. Drews 187
High-Resolution C r y s t a l S t r u c t u r e of C-Phycocyanin and Polarized O p t i c a l Spectra of Single C r y s t a l s by T. Schirmer, W. Bode and R. Huber 195
C r y s t a l l i z a t i o n and Spectroscopic I n v e s t i g a t i o n of Purple B a c t e r i a l B800-850 and RC-B875 Complexes by W. Welte, Τ. Wacker and A. Becker 201
S t r u c t u r e of the Light-Harvesting Chlorophyll a/b-Protein Complex from Chloroplast Membranes by W. Kühlbrandt 211
PhycobiIi somes of Synchechococcus Sp. PCC 7002, Pseudanabaena Sp. PCC 7409, and Cyanopnora paracioxa: An "Analysis by" HoTecular Genetics by D.A. Bryant 217
Organization and Assembly of B a c t e r i a l Antenna Complexes by G. Drews 233
IX
The Use of Mutants t o Inv e s t i g a t e the Organization of the Photosynthetic Apparatus of Rhodobacter sphaeroides by C.N. Hunter and R. van Grondel l e 77.77 247
Mechanisms of P l a s t i d and Nuclear Gene Expression During Thylakoid Membrane Biogenesis i n Higher Plants by P. Westhoff, Η. Grüne, Η. Schrubar, Α. Oswald, Μ. Streubel, U. Ljungberg and R.G. Herrmann 261
SECTION I I I : ORGANIZATION: SPECIAL SPECTROSCOPY TECHNIQUES AND MODELS
Assigment o f Spectral Forms i n the Photosynthetic Antennas to Chemically Defined Chromophores by A. Scherz 277
Linear Dichroism and Or i e n t a t i o n of Pigments i n Phycobilisomes and t h e i r Subunits by L. Juszcak, N.E. Geacintov, B.A. Z i l i n s k a s and J. Breton 281
Low Temperature Spectroscopy of Cyanobacteria! Antenna Pigments by W. Köhler, J. F r i e d r i c h , R. Fischer and H. Scheer 293
Chromophore Conformations i n Phycocyanin and Allophycocyanin as Studied by Resonance Raman Spectroscopy by B. S z a l o n t a i , V. Csizmadia, Z. Gombos, K. Csatorday and M. Lutz 307
Coherent Anti-Stokes Raman Spectroscopy of Phycobi1isomes, Phycocyanin and Allophycocyanin from Mastigocladus laminosus by S. Schneider, F. Baumann, W. Steiner, R. Fischer, S. Siebzehnrlibl and H. Scheer 317
Op t i c a l Absorption and C i r c u l a r Dichroism of Bacteriochlorophyl1 Oligomers i n T r i t o n X-100 and i n the Light-Harvesting-Complex B850; A Comparative Study by V. Rozenbach-Belkin, P. Braun, P. Kovatch and A.Scherz 323
Absorption Detected Magnetic Resonance i n Zero Magnetic F i e l d on Antenna Complexes from Rps. acidophila 7050 - The Temperature Dependence of tfie CarotenoTiTTrTpTet State Prop e r t i e s by J. U l l r i c h , J.U. v. Schütz and H.C. Wolf 339
E f f e c t o f Li t h i u m Dodecyl S u l f a t e on Β 800-850 Antenna Complexes from Rhodopseudomonas acidophila: A Resonance Raman Study by B. Robert and H. Frank 349
χ
B a c t e r i o c h l o r o p h y l 1 a/b i n Antenna Complexes of Purple Bacteria by Β. Robert, A. Vermeglio, R. Steiner, Η. Scheer and Μ. Lutz 355
B a c t e r i o c h l o r o p h y l l c Aggregates i n Carbon T e t r a c h l o r i d e as Models f o r Chlo r o p h y l l Organization i n Green Photo­ s y n t h e t i c B acteria by J.M. Olson and J.P. Pedersen 365
O r i e n t a t i o n o f t he Pigments i n the Reaction Center and the Core Antenna o f Photosystem I I by J. Breton, J. Duranton and K. Satoh 375
Non-Linear Absorption Spectroscopy of Antenna Chlorophyll a in Higher Plants by D. Leupold, H. S t i e l and P. Hoffmann 387
SECTION IV: FUNCTION: ELECTRONIC EXCITATION AND ENERGY TRANSFER
E x c i t a t i o n Energy Transfer i n Photosynthesis by R. van Grondelle and V. Sundström 403
Fluorescence Spectroscopy of Allophycocyanin Complexes from Synechococcus 6301 S t r a i n AN112 by P.Maxson, KTTauer and A.N. Glazer 439
Picosecond Energy Transfer K i n e t i c s i n Allophycocyanin Aggregates from Mastigocladus laminosus by E. Bittersmann, W. Reuter, W. Wehrmeyer and A.R. Holzwarth 451
Picosecond Time-Resolved Energy Transfer K i n e t i c s w i t h i n C-Phycocyanin and Allophycocyanin Aggregates by T. G i l l b r o , A. Sandström, V. Sundström, R. Fischer and H. Scheer 457
Energy Transfer i n "Native" and Chemically Modified C-Phyco­ cyanin Trimers and the Constituent Subunits by S. Schneider, P. Gei s e l h a r t , F. Baumann, S. Siebzehnrübl, R. Fischer and Η. Scheer 469
E f f e c t of P r o t e i n Environment and Exc i t o n i c Coupling on the Excited-State Pro p e r t i e s of the Bilinchromophores i n C-Phycocyanin by S. Schneider, Ch. Scharnagl, M. Dürring, T. Schirmer and W. Bode 483
E x c i t a t i o n Energy M i g r a t i o n i n C-Phycocyanin Aggregates I s o l a t e d from Phormidium luridum: P r e d i c t i o n s from the Förster's I n d u c t i v e Resonance Theory by J. Grabowski and G.S. Björn 491
XI
Energy Tra n s f e r Calculations f o r two C-Phycocyanins Based on Refined X-Ray Crystal S t r u c t u r e Coordinates of Chromophores by K. Sauer and H. Scheer 507
Energy Transfer i n Light-Harvesting Antenna o f Purple B a c t e r i a Studied by Picosecond Spectroscopy by V. Sundström, H. Bergström, Τ. G i l l b r o , R. van Grondelle, W. Westerhuis, R.A. Niederman and R.J. Cogdell 513
E x c i t a t i o n Energy Transfer i n the Light-Harvesting Antenna o f Photosynthetic Purple B a c t e r i a : The Role of the Long-Wave- Length Absorbing Pigment B896 by R. van Grondelle, H. Bergström, V. Sundström, R.J. van Dorssen, M. Vos and C.N. Hunter 519
The Function o f Chlorosomes i n Energy Transfer in Green Photo­ s y n t h e t i c Bacteria by R.J. van Dorssen, M. Vos and J. Amesz 531
Energy Transfer i n Chloroflexus aurantiacus: E f f e c t s of Temperature and TSaerobic^onönHons by B.P. Wittmershaus, D.C. Brune and R.E. Blankenship 543
I n t e r p r e t a t i o n o f Optical Spectra of Bacteriochlorophyl 1 Antenna Complexes by R.M. P e a r l s t e i n 555
Time Resolution and K i n e t i c s o f "F680" a t Low Temperatures i n Spinach Chloroplasts by R. Knox and S. L i n 567
Picosecond Studies of Fluorescence and Absorbance Changes i n Photosystem I I P a r t i c l e s from Synechococcus Sp. by A.R. Holzwarth, G.H. Schatz and H. Brock 579
Analysis of E x c i t a t i o n Energy Transfer i n Thylakoid Membranes by the Time-Resolved Fluorescence Spectra by M. Mimuro 589
V. CONCLUDING REMARKS
by E. Gantt 601
and Marc LUTZ
: S e r v i c e de Biophysique, Departement de Biologie, C.E.N. Saclay, 91191 G i f s u r Yvette CEDEX FRANCE **
: A.R.B.S., CEN Cadarache, B.P.I, St Paul Lez Durance, + : Botanisches I n s t i t u t der Universität München, D 8000 München
1 9 , GFR
I n t r o d u c t i o n
During the l a s t f i v e years, d e c i s i v e progresses has been made i n the knowledge of the s t r u c t u r e s of the protein-pigment complexes involved i n the f i r s t s t e p s of b a c t e r i a l photosynthesis. However, t h i s progress has l a r g e l y concerned r e a c t i o n centers ( 1 ) , and has been slower f o r l i g h t h a r v e s t i n g complexes. As f a r as R h o d o s p i r i l l a l e s (purple b a c t e r i a ) are concerned, the two subunits of many Β 870 and Β 8 5 0 - 8 0 0-type antenna complexes have now been sequenced ( 2 ) . However, up u n t i l now, none of the s e v e r a l c r y s t a l l i z a t i o n attempts yet allowed a h i g h l y d i f f r a c t i n g c r y s t a l s to be obtained. Resonance Raman spectroscopy i s thus c u r r e n t l y the only method able to provide information about the s t r u c t u r e of these complexes. Thi s technique indeed permits s e l e c t i v e observation of the 'active s i t e ' of the antenna, i . e . , the regions of the proteins which bind the BChl molecules and are r e s p o n s i b l e f o r t h e i r e l e c t r o n i c absorption p r o p e r t i e s : studying the Raman-active v i b r a t i o n modes of BChl within the n a t i v e l i g h t h a r v e s t i n g pigment-protein complexes indeed permits to c h a r a c t e r i z e s e v e r a l of the i n t e r a c t i o n s occurring between these pigments and t h e i r micro-environment, and thus gives some i n d i c a t i o n s of the s t r u c t u r e s of BChl host s i t e s w i t h i n the protein. I n t h i s a r t i c l e , we w i l l b r i e f l y summarize conclusions r e c e n t l y drawn from
Photosynthetic Light-Harvesting Systems © 1988 Walter de Gruyter & Co., Berlin · New York
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resonance spectroscopy of BChl a and b-containing complexes of R h o d o s p i r i l l a l e s .
Resonance Raman Spectroscopy of Antenna complexes from R h o d o s p i r i l l a l e s
E x c i t a t i o n of both BChl a and BChl b near the tops of t h e i r Soret t r a n s i t i o n s provides resonance Raman spectra which contain much
s t r u c t u r a l information (3,4,5). The 1620-1720 cm"1 regions of the Raman spectra obtained i n these conditions of resonance contain bands a r i s i n g from the s t r e t c h i n g modes of the 2-acetyl and 9-keto carbonyl groups, which are conjugated with the dihydrophorbin c y c l e s of the molecules. The frequencies of these modes are s e n s i t i v e to existence and strength of intermolecular bonds i n which these chemical groups may be engaged (6) : t y p i c a l l y , 2-acetyl groups of BChl a and b
v i b r a t e s a t 1665 cm 1 and 1670 cm 1 r e s p e c t i v e l y when fr e e from intermolecular bonding. These frequencies may s h i f t down to ca 1630 when the groups assumes hydrogen bonding ( 6 ) . The 9-keto groups of
both BCH1 a and b v i b r a t e s near to 1700 cm"1 when f r e e from intermolecular i n t e r a c t i o n s , and t h e i r s t r e t c h i n g frequency may s h i f t
down to 1660 cm 1 when they are hydrogen bonded ( 6 ) . Moreover, i n the same s p e c t r a l region, the frequency of a band located near to
1600 cm"1 , and which mainly a r i s e s from methine bridge s t r e t c h i n g , i s s e n s i t i v e to the number of a x i a l ligands t h a t bind the c e n t r a l Mg of the molecule f o r both BChl a and b ( 6 ) . T h i s band indeed occurs a t
1600 cm"1 when two a x i a l ligands are bound to the Mg atom, and
around 1615 cm"1 when i t i s five-coordinated. Thus, s p e c t r a l
a n a l y s i s of the 1550-1750 cm"1 region brings information about the i n t e r a c t i o n s t a t e s of the c e n t r a l Mg and of both the conjugated C=0 of BChl a or b. These groups are known to be predominantly involved i n intermolecular i n t e r a c t i o n s of ch l o r o p h y l l s both i n vivo and i n v i t r o ( 6 ) .
357
Core antenna (B 890,870 complexes)
The very c l o s e s i m i l a r i t y of resonance Raman spectra of core antenna complexes from any species of R h o d o s p i r i l l a l e s that wa have studied so f a r i n d i c a t e s that, i n a l l these complexes, the p r o t e i c host s i t e s of BChl are extremely s i m i l a r , most probably providing the same binding groups to the conjugated carbonyls of BChl a molecules ( 3 ) . For more than ten species and s t r a i n s (Rhb sphaeroides, capsulatus, Rps p a l u s t r i s , acidophila, Rsp rubrum, Chromatium vinosum Thiocapsa r o s e o p e r s i c i n a ) the RR spectra of the core antenna obtained at Soret resonance are extremely s i m i l a r to that presented i n f i g l a . The
strong 1645 cm""1 band most probably a r i s e s from both of the a c e t y l c a r bony 1 groups of both of the BChl a molecules known to be present i n Β 870-type complexes. These groups thus assume s i m i l a r i f not i d e n t i c a l intermolecular i n t e r a c t i o n s . The frequency of t h i s band i s species-dependent, being up or downshifted by a few wavenumbers from
the 1645 cm"1 mean value. These v a r i a t i o n s l i k e l y a r i s e from s l i g h t v a r i a t i o n s i n the environment or geometry of the intermolecular C=0 - — X bond r a t h e r than from a v a r i a b i l i t y i n the nature of the s i t e X. Two bands are observed i n the keto s t r e t c h i n g region of RR spectra : i n t e r a c t i o n s assumed by keto groups of both BChl i n Β 870-type are thus not the same. However both of them are most probably H-bonded,
v i b r a t i n g r e s p e c t i v e l y a t 1667 and 1678 cm""1 . The 1615 cm"1
frequency of the me thine bridge s t r e t c h i n g mod© c l e a r l y i n d i c a t e s that, i n Β 880-type complexes as w e l l as i n any BChl-containing antenna complexes studied to date (3,4,5), the c e n t r a l magnesiums of the BChls are five-coordinated.
P e r i p h e r i c antenna (B 850-800 or 820-800-type complexes)
From the BChl h o s t - s i t e s t r u c t u r e s revealed by RR spectroscopy a t
358
l e a s t two f a m i l i e s must be disti n g u i s h e d among the Β 850-800-type complexes : intermolecular i n t e r a c t i o n s assumed by the three BChl i n Β 850-800 complexes extracted from Rhodospirillaceae indeed d i f f e r from those extracted from Chromatiaceae ( f i g 2) ( 3 ) . I n RR spectra of Β 850-800 complexes from Chromatiaceae, the C=0 s t r e t c h i n g modes
consitute as a complex c l u s t e r located around 1656 cm""1 , with a
shoulder at 1671 cm"1 , and in v o l v i n g very weakly bound a c e t y l and H- bonded keto groups. RR spectra of the Rhodospirillaceae complexes, e x h i b i t resolved bands at 1633, 1641, 1666-1670 and o c c a s i o n a l l y 1700
cm 1 . Moreover, i n t e r g e n e r i c v a r i a b i l i t y has been observed among the RR spectra of Β 850-800 complexes from Rhodospirillaceae thus revealing i n t e r g e n e r i c s t r u c t u r a l v a r i a b i l i t y ( 4 ) : i n RR spectra of the Β 850- 800 complexes extracted from b a c t e r i a of the Rhodobacter genus (sphaeroides, c a p s u l a t u s ) , the keto C=0 group of the 800-nm absorbing
BChl i s f r e e from intermolecular bonding, v i b r a t i n g a t 1700 cm"1
whereas i t i s intermolecularly bound i n Β 850-800 complexes of b a c t e r i a from the Rhodopseudomonas genus ( p a l u s t r i s , acidophila, type I I complexes). Thi s i n t e r g e n e r i c v a r i a b i l i t y i s a l s o observed f o r the a c e t y l groups of the 800 nm-absorbing and one of one of the 850 nm- absorbing BChls. I n t h i s case only changes i n the strengths of the intermolecular i n t e r a c t i o n s of these groups are observed. Two types of Β 850-800 complexes have been extracted from Rps acid o p h i l a (type I and type I I ( 7 ) ) . Host s i t e s of BChls w i t h i n type I complexes are very s i m i l a r to those of Β 850-800 complexes extracted from the Rhodobacter genus (B. ROBERT and R.J. C0GDELL, unpublished r e s u l t s ) . Β 830-800 complexes (or 'high 800nm-absorbing complexes') have been p u r i f i e d from b a c t e r i a of the Rhodopseudomonas genus grown i n low l i g h t . These complexes e x h i b i t absorption s p e c t r a very s i m i l a r to those of Β 850-800 complexes extracted from Chromatiaceae. However, on the b a s i s of the s t r u c t u r e s of the BChl host s i t e s , revealed by RR spectroscopy, these complexes appear to be a c t u a l l y r e l a t e d to 'regular' Β 850-800 complexes of Rhodospirillaceae, genus RhcKiopseudomonas, from which they appear to only d i f f e r by the presence of an a d d i t i o n a l BChl molecule ( 4 ) .
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Fig 2 : RR spectra (363.8 nm excitation) of I a) (lower trace) Β 850-800 from Chromatiura vinosum b) (middle trace) Β 850-800 from Chromatium tepidum Wavenumber (cm ) c) (upper t r a c e ) Β 850-800 type I from Rps acidophila
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The thermophilic bacterium Chromatium tepidum
We have studied antenna complexes extracted from the thermophilic bacterium Chromatium tepidum : t h i s bacterium s y n t h e s i z e s both a core antenna (B 920) and a p e r i p h e r i c one (B 855-800) which are thermostable up to 70 C i n the i n t a c t membrane ( 8 ) . I n both these complexes, the c e n t r a l magnesiums of a l l of the BChl molecules are five-coordinated, as i n the mesophilic s t r a i n s . On the other hand, i n
both of these complexes, a ca 13 cm"1 downshift of the whole set of frequencies of the a c e t y l carbonyl v i b r a t o r s i s observed, i n d i c a t i n g that these groups are a l l engaged i n stronger intermolecular i n t e r a c t i o n s than i n the mesophilic Chromatium vinosum s t r a i n . At
such wavenumbers, a 13 cm"1 downshift of a C=0 v i b r a t o r approximately corresponds to an i n c r e a s e i n H-bond strength of 2 kcal/M. I n Β 920 complexes, the keto carbonyl s t r e t c h i n g frequencies
are a l s o downshifted (16 cm"1 ) r e l a t i v e to the mesophilic s t r a i n . Hence, i n antenna complexes extracted from t h i s thermophilic s t r a i n , p r o t e i c host s i t e s appear to provide BChl molecules with noticeably stronger i n t e r a c t i o n s on most of t h e i r conjugated carbonyls. Following suggestion by BABCOCK and CALLAGHAN (9) i t would be tempting to r e l a t e the 880->920 nm absorption d i f f e r e n c e to the d i f f e r e n c e i n l i g a t i o n strength of the carbonyl groups of the BChls i n the core complexes of the mesophilic and thermophilic s p e c i e s . Nevertheless, the liganding of these groups ( a t l e a s t of the a c e t y l ones) appears to have only a l i m i t e d i n f l u e n c e on the e l e c t r o n i c absorption of the pigments s i n c e the p e r i p h e r i c antennae of both tepidum and vinosum species e x h i b i t the same absorption spectra, whereas the l i g a t i o n strength of the a c e t y l carbonyl of t h e i r BChl a a l s o d i f f e r by hte same amounts.
BChl b-Containing Antenna Complexes
Core antenna of Rps v i r i d i s (Β 1015) RR s p e c t r a of Behl b-containing antenna i n d i c a t e t h a t , as i n the case
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of BChl a-containing complexes, the c e n t r a l Mg of the pigments within these complexes generally are s i n g l y liganded (methine bridge
frequency a t 1615 cm" 1). However, the l i g a t i o n of BChl b i n Β 1015 from Rps v i r i d i s appears to be d i f f e r e n t from that of BChl a i n Β 880- type complexes : indeed, i n the carbonyl s t r e t c h i n g region of the
former complex, a weak 1639 cm"1 a r i s e s from a H-bonded a c e t y l C=0,
a strong 1670 cm 1 most probably a r i s e s from a f r e e a c e t y l group and
from a Η-bonded keto grouping, and a 1682 cm 1 , band a r i s e s from a weakly i n t e r a c t i n g keto carbonyl ( f i g l c ) .
Β 800-1020 complex from Ectothiorhodospira h a l o c h l o r i s
Β 800-1020 complex from Ectothiorhodospira h a l o c h l o r i s i s a BChl b- containing core antenna. Biochemical a n a l y s i s (10) i n d i c a t e d t h a t i t contains f i v e BChl b, two of them being responsible f o r the 1015 nm absorption peak. RR data l a r g e l y confirm these hypothesis : a t l e a s t four unequivalently i n t e r a c t i n g BChl b are present i n these complex, as f a r as 8 d i f f e r e n t frequencies may be observed i n the C=0 s t r e t c h i n g region. Moreover, HCl-treatment, which r e s u l t s i n s h i f t i n g the 1015 nm t r a n s i t i o n down to 960 nm (10), a f f e c t s the s t r e t c h i n g v i b r a t i o n s of no more than two a c e t y l and two keto carbonyl groups.
Overview
RR spectroscopy shows that, although the sequences of antenna complexes of purple b a c t e r i a appear to be h i g h l y conservative ( 2 ) , i n t e r a c t i o n s assumed by BChls i n many of these complexes are l a r g e l y s p e c i e s - (or genus-) dependent. Despite t h i s i n t e r s p e c i f i c v a r i a b i l i t y , antenna complexes of purple b a c t e r i a share common s t r u c t u r a l f e a t u r e s at t h e i r a c t i v e s i t e s :
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- a l l BChl molecules have s i n g l y liganded Mg. From both sequence data and RR spectra ( 3 ) , these ligands are most probably imidazole si d e chains of h i s t i d i n e s i n most cases. The 800 nm-absorbing BChl of Rhb sphaeroides Β 850-800 complexes may c o n s t i t u t e an exception i n t h i s respect.
- I n a l l of these complexes, BChl appears not to be d i r e c t l y exposed to the l i p i d i c phase or aqueous detergent : indeed, RR spectra are i n s e n s i t i v e to the i s o l a t i o n procedures, to the nature of the detergent as w e l l as to the s i z e of the complex multimers. Moreover, when d i r e c t comparison are p o s s i b l e (Rsp rubrum) RR spectra of the membrane-bound and extracted complexes are i d e n t i c a l . Now that s e v e r a l sequences are a v a i l a b l e f o r (2) antenna complexes of purple b a c t e r i a hypotheses can be drawn from RR spectroscopy about the nature of the aminoacids i n t e r a c t i n g with the pigments For example, Β 1015 complex from Rps v i r i d i s i s the only core antenna for
which no 1645 cm"1 RR band i s observed but for which 1639 cm - 1 and 1670 bands are observed. This s p e c i f i c i t y may w e l l be r e l a t e d to the f a c t that i t s polypeptides each have s p e c i f i c amino a c i d changes r e l a t i v e to a l l of the other polypeptides of core antenna : phenylalanine -8 (taking the conserved His as 0 p o s i t i o n ) i n the alpha polypeptide i s replaced i n v i r i d i s by a t y r o s i n e which could provide a Η-bond to the C=0 a c e t y l group so that i t s frequency could
be downshifted to 1639 cm"1 ? i n the beta one the +6 Trp i s a l s o replaced by an Ala. These aminoacids are thus l i k e l y candidates as binding s i t e s of a c e t y l C=0 groups. S i m i l a r l y , when more antenna complex polypeptides are sequenced, i t w i l l most probably be p o s s i b l e to locate the BChl molecules i n the polypeptide matrix taking i n t o account both o r i e n t a t i o n s of e l e c t r o n i c t r a n s i t i o n moments and RR data.
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References
1) MICHEL, Η., EPP, 0. and DEISENHOFER, J . (1986) EMBO J . 5-10 2445- 2451
2) ZUBER, Η., SIDLER, W., FUGLISTALLER, P., BRUNISHOLZ, R. and THEILER, R. (1987) Trends i n Biochem. Sc., 11, 414-419
3) ROBERT, B. and .LUTZ, Μ. (1985) Biochim. Biophys. Acta 807, 10-23
4) ROBERT, B. ANDRIANAMBININTSOA, S. and .LUTZ, Μ. (1985) Biophys J . (Tokyo), 100, 6-11
5) ROBERT, B., STEINER, R., ZHOU, Q., SCHEER, H. and LUTZ, Μ. (1987) i n : Progess i n Photosynthesis Research (BIGGINS, J . ed) Martinus Nijhoff, Dordrecht, The Netherlands
6) LUTZ, Μ. and ROBERT, B. (1987) i n B i o l o g i c a l a p p l i c a t i o n s of Raman spectroscopy (SPIRO, T.G. ed) Vol I I I Chap 9
7) C0GDELL, R.J., DURANT, I . , VALENTINE, J . , LINDSAY, J.G. and SCHMIDT, K. (1983) Biochim. Biophys. Acta 722, 427-455
8) MADIGAN, M.T. (1984) Science 225, 313-315
9) CALLAGHAN, P.M. and BABCOCK, G.T. (1983) Biochemistry 22, 452-461