Intramolecular Allosteric Communication in Dopamine D2 Receptor Revealed by Evolutionary Amino Acid Covariation
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Intramolecular allosteric communication in dopamine D2 receptor revealed by evolutionary amino acid covariation Yun-Min Sunga, Angela D. Wilkinsb, Gustavo J. Rodrigueza, Theodore G. Wensela,1, and Olivier Lichtargea,b,1 aVerna and Marrs Mclean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030; and bDepartment of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030 Edited by Brian K. Kobilka, Stanford University School of Medicine, Stanford, CA, and approved February 16, 2016 (received for review August 19, 2015) The structural basis of allosteric signaling in G protein-coupled led us to ask whether ET could also uncover couplings among receptors (GPCRs) is important in guiding design of therapeutics protein sequence positions not in direct contact. and understanding phenotypic consequences of genetic variation. ET estimates the relative functional sensitivity of a protein to The Evolutionary Trace (ET) algorithm previously proved effective in variations at each residue position using phylogenetic distances to redesigning receptors to mimic the ligand specificities of functionally account for the functional divergence among sequence homologs distinct homologs. We now expand ET to consider mutual informa- (25, 26). Similar ideas can be applied to pairs of sequence positions tion, with validation in GPCR structure and dopamine D2 receptor to recompute ET as the average importance of the couplings be- (D2R) function. The new algorithm, called ET-MIp, identifies evolu- tween a residue and its direct structural neighbors (27). To measure tionarily relevant patterns of amino acid covariations. The improved the evolutionary coupling information between residue pairs, we predictions of structural proximity and D2R mutagenesis demon- present a new algorithm, ET-MIp, that integrates the mutual in- strate that ET-MIp predicts functional interactions between residue formation metric (MIp) (5) to the ET framework. We used dopa- pairs, particularly potency and efficacy of activation by dopamine. mine D2 receptor (D2R), a target of drugs for neurological and Remarkably, although most of the residue pairs chosen for mutagen- psychiatric diseases (28), to test whether ET-MIp could elucidate the esis are neither in the binding pocket nor in contact with each other, allosteric functional communications from amino acid covariation many exhibited functional interactions, implying at-a-distance cou- patterns and resolve the evolutionary distance at which the allosteric pling. The functional interaction between the coupled pairs corre- pathways of D2R homologs are sufficiently conserved to detect res- lated best with the evolutionary coupling potential derived from idue−residue coupling signatures. D2R is expressed in the central dopamine receptor sequences rather than with broader sets of GPCR nervous system and responds to dopamine, the major catecholamine sequences. These data suggest that the allosteric communication re- neurotransmitter. Canonical D2R signaling is effected by G class sponsible for dopamine responses is resolved by ET-MIp and best i/o G proteins, which regulate ion channels (29, 30), MAPK kinases discerned within a short evolutionary distance. Most double mutants restored dopamine response to wild-type levels, also suggesting that (31), phospholipase C (32), and inhibition of adenylyl cyclase (33). D1 class receptors (D1R and D5R) have lower affinities for tight regulation of the response to dopamine drove the coevolution – and intramolecular communications between coupled residues. Our dopamine (34 36) and activate adenylyl cyclase through Gs class G approach provides a general tool to identify evolutionary covariation proteins. To characterize allosteric communication between patterns in small sets of close sequence homologs and to translate them into functional linkages between residues. Significance allostery | G protein-coupled receptors | residue covariation | Characterizing relationships among protein structure, function, Evolutionary Trace and evolution requires understanding the evolutionary con- straints on each constituent residue of a protein. Previous dentifying residues that coevolved to maintain or acquire fit- studies have shown that structural information can be re- Iness properties is critical for understanding protein structure, trieved from evolutionary residue covariation in protein fami- function, and evolution (1). Previous studies have shown that lies. However, whether the evolutionary history in protein covarying residue pairs, those that exhibit correlated amino acid sequences informs on functional interactions between non- changes in large multiple sequence alignments, tend to form adjacent residues has been unclear. Here, we developed a structural contacts (2–7), enhancing predictions of protein 3D method that uses evolutionary amino acid covariation to infer BIOPHYSICS AND structures (8–11). Covariation can also involve distal residues, functionally coupled residue pairs in the dopamine D2 receptor. but the function of these at-a-distance couplings is elusive and We discovered functional coupling between residue pairs that COMPUTATIONAL BIOLOGY has been attributed to background noise, alternative protein have coevolved mainly to control responses to dopamine and conformations, or subunit interactions of protein homooligomers maintain them at wild-type levels. Our findings demonstrate the (5, 7, 12). Alternately, distal covarying residue pairs could in- possibility of extracting the networks of intramolecular allosteric dicate allosteric couplings (6, 13–18). communication from evolutionary residue covariation patterns. The possibility of capturing intramolecular allosteric communi- Author contributions: Y.S., A.D.W., T.G.W., and O.L. designed research; Y.S. and A.D.W. cation by amino acid covariation analysis of protein family se- performed research; Y.S., A.D.W., and G.J.R. contributed new reagents/analytic tools; Y.S., quences has not been extensively explored. Nonproximal A.D.W., T.G.W., and O.L. analyzed data; and Y.S., A.D.W., T.G.W., and O.L. wrote thermodynamic coupling between correlated residue pairs was the paper. noted in 274 PDZ domains (14), but the relationship to allo- The authors declare no conflict of interest. stery is still debated (19, 20). It may be that distinctive allosteric This article is a PNAS Direct Submission. mechanisms, even among close homologs, limit the extraction Freely available online through the PNAS open access option. of allosteric couplings from sequences (13). Our previous identi- 1To whom correspondence may be addressed. Email: [email protected] or twensel@ fication of residues important for allosteric signaling within G bcm.edu. protein-coupled receptors (GPCRs) using Evolutionary Trace (ET) This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. (21–24) and strong conservation of some of the residues implicated 1073/pnas.1516579113/-/DCSupplemental. www.pnas.org/cgi/doi/10.1073/pnas.1516579113 PNAS | March 29, 2016 | vol. 113 | no. 13 | 3539–3544 Downloaded by guest on September 26, 2021 covarying pairs of residues ranked as important by ET (ET residue functional allostery in D2R, tuned to a specific ligand and sig- pairs), we examined functional coupling for ligand binding affinities naling bias, a more restricted alignment may be best. Accord- and downstream Gi activation induced by agonist-stimulated D2R. ingly, multiple alignments were tested (Class A, bioamine, dopamine, and D2Rs) and yielded distinct coupling scores Results (Table S2). ET-MIp Identified Pairs of Residue Positions with Evolutionary Covariation Patterns. We hypothesized that accounting for spe- Functional Interactions Between Covarying ET Residue Pairs Maintained cies divergence would improve the detection of functionally Dopamine Response at WT Level. To test whether the selected ET coupled residues over covariation analyses that ignore phyloge- residue pairs were functionally coupled, we first compared the netic information. ET-MIp adds the mutual information metric effects of single and double mutations on dopamine efficacy using (5) to ET to keep track of the phylogenetic distance at which a a fluorescence-based assay to study Gi activation induced by pair of residues vary (Fig. 1A; see Materials and Methods and agonist-stimulated D2R (Fig. 2; see Materials and Methods and Supporting Information for details). In ∼2,500 Class A GPCR Supporting Information for details). For five pairs (V83L2.53/ transmembrane (TM) domain sequences, we found that residue V91S2.61, M117F3.35/Y199F5.48, I48T1.46/F110W3.28,V152A4.42/ 4.61 3.42 5.54 pairs with high ET-MIp scores were more enriched for direct L171P , and N124H /T205M ), activation of Gi in re- contacts in a reference structure (PDB 2RH1) compared with sponse to dopamine was unexpectedly decreased or restored to a results obtained with leading alternative methods (5, 37, 38) (Fig. near-wild-type (WT) level in the double mutants, even though 1B), showing that GPCR phylogenetic information improves the one or both of the constituent single mutants showed signifi- coupling signal. Preliminary analysis of other protein families cantly enhanced response (Fig. 2 A and C). These results in- suggests that this result may be fairly general. This opens the dicate that covarying ET residue pairs help maintain dopamine possibility that ET-MIp also detects functionally relevant co- responses at the WT level. A trend was that functional coupling