A regulator of G protein signaling interaction surface linked to

effector specificity4/24/2008

Heterotrimeric G Proteins

• Secondary messenger protein in various tissues from the heart to the eye

• Important for drug development• “GPCRs (G-Protein Coupled Receptors) are targeted by 12 of the

top 20 selling drugs, including Coreg for congestive heart failure, Cozaar for high blood pressure, Zoladex for breast cancer, Buspar for anxiety and Clozaril for schizophrenia, as well as by Zantac and Claritin. Together the drug class accounts for $200bn (€159 bn) in annual sales.” - Chu, 2006

G Proteins continued• Regulator of G Protein

Signaling (RGS) increases rate of GTP hydrolysis by G-GTP, speeding up system

How is RGS specificity maintained?

• There are over 50 RGS proteins identified with a variety of activities and sequences.

• Crystal structure shows contact residues are highly conserved between RGS and G suggesting other partners.

• What region provides this specificity?

Evolutionary Trace Method

• Input: Aligned protein family sequences, evolutionary tree and protein structure

• Output: Ranking of evolutionary importance visually represented on the protein structure

Evolutionary Trace Method

• 1) Subdivide protein family sequence into groups based on evolutionary tree branches

E.T. Method Continued

• 2) At each trace level, refer back to the alignment and report the conservation of residues within each subgroup

E.T. Method Continued

• 3) If a position is invariant in a subgroup but differs between subgroups. It is a Class-Specific residue.

E.T. Method Continued

• This process can be repeated until all positions receive a rank.

• Residues with lower ranks are considered more important.

ET of RGS Protein Family• Result of

ET method yields initial contact residues and putative binding surface

Evolutionarily Privileged Surface of the RGS Domain

• Secondary Structure Residues are non-contiguous but cluster spatially

• Surface containing both invariant and class-specific residues

Cluster of class-specific residues at the RGS-G interface

• RGS protein in white

• G shown in yellow

• Invariant in red

• Class specific blue

• B is the newly identified residues, shape suggests location for binding

Correlation of ET identified RGS residues with PDE-y effects

RGSprotein PDE-y effect*

ET identified residuenumber (based on theRGS4)

77 117 121 122 124 126 134

RGS4 Inhibit Lys Glu- Val Gln Thr Glu Arg

RGS16 Inhibit His Glu- Ser Glu Pro Glu Arg

GAIP Inhibit Arg Asp- Ile Leu Pro Glu Arg

RGS6 Inhibit Leu Glu- Pro Gly Pro Ala Tyr

RGS9 Enhance Gln Leu Pro Gly Arg Trp Met

RGS11 None Met Gln Pro Gly Ala Trp Met

• Example: 117, - inhibits, non-polar enhances, non-charged polar has no effect

Modulation of RGS GAP by PDEy

• GTPase accelerating protein (GAP) modulation is a phenotype used to compare taxa

Class specific residues cluster near putative PDE-y binding site

• When mapped to the structure, the class-specific residues are located on a contiguous range providing a putative PDE-y binding site

Conclusions

• The evolutionary trace method can identify functionally important residues within a protein structure.

• The ET of the RGS protein family confirmed 10 of 11 previously identified contact residues and discovered a cluster of class specific residues which could function as a binding domain for PDE-y to control RGS GAP activity.