GPCR's in a nut shell

30 % of the genome codes for membrane proteins

The GPCR superfamily is the largest among the membrane proteins.

More than 50% of the drugs targets are focussed on GPCR's

In 2003 the worldwide sales reached $47 billion

Why? GPRC transduce extracellular signal into de cell in diverse physiological preccesses

such as:Neurotransmission, cellular metabolism, hormone

secretion, cell growth, and immune defense among

others.

The top 200 selling drugs are based on GPCR.

Family A:

light, adrenaline

and olfactory receptors.

Family B:

secretin, glucagon,

calcitonin,corticotrophin

R-hormone and vasoactive

intestinal peptides receptors.

Family C:

GABA, metabotropic

glutamate, calcium-sensing

and certain taste receptors.

Rhodopsin: opsin+retinal

Rh is involved in the molecular

transformation of light into a

neuronal signal.

348 residues

Function:

Structure

7 TM helices + 1 cytoplasmic helix

Motif DRY where D is forming double

Salt bridge with E134 and E247

PDB: 1F88(2.8 A), 1U19(2.2 A)

Palczewski K, et al. (2000) Science 289:739

Important for maintaining the inactive

states

Extracellular loops (EL) well packed

Intracellular loops (IL) coiled and with high

B-factors.

Disulfide bridge C187-C110

2167 times cited

Vision Cycle:

+

photon

H20+

twist angles at C11-C12 (-18 )

C11C12

The torsion in the C11-C12 bond might be a pre-requisite for the isomerization process.

Okada T. et al. (2004) JMB 342:571

Water network in rhodopsin

NH+ of the Schiff base group at H-bond

distance of COO- of Glu113.

Thr94, Ser186 and Wat2b form

a hydrogen bonding network

involving Glu113.

Wat2a extends the hydrogen bond to Glu181.

The network continues up to Tyr268 and

Tyr192. This network might a possible path for

the switch of counterion in metarhodopsin I.

Squid rhodopsin

448 residues

7 TM helices + 2 cytoplasmic

helices

TM5 and TM6 show a 25 A extension

into the cytosol..

TM6 interacts with C-terminus and

Helix-9.

The rigid conformation in the cytosol

might be a structural motif associated

binding to specific G-proteins.

Disulphide bridge C186-C108

Helix-8 is anchored to the membrane

by a palmitoyl group bonded to Cys337

Protein-protein interaction in the crystal

structure is mediated by a phospholipid

in the extracellular interface

The retinal is bonded to Lys 305 and shows a U shape

around the Trp274 ring.

There are five aromatic rings close to the retinal.

The residues in contact with retinal show significant

differences with respect to bovine rhodopsin.

Glu180 is far away from retinal. Instead,

Asn185 might mediate the interaction between

retinal and Glu180 after photoisomerization.

Retinal environment in squid rhodopsin

Retinal interactions Water network

Larger amount of water molecules in the interhelical cavity than in bovine rhodopsin.

Evidence of the change of vibrational frequencies of more than eight water molecules

on formation of bathorhodopsin.

Final remarks

New insights for the activation of membrane proteins can be addressed from the

molecular dynamics simulation of squid rhodopsin.

Light induce conformational changes in squid rhodopsin and the signal propagates

towards the cytoplasmic side along the water cluster located in the interhelical domain.