1
|
O'Neil PT, Swint‐Kruse L, Fenton AW. Rheostatic contributions to protein stability can obscure a position's functional role. Protein Sci 2024; 33:e5075. [PMID: 38895978 PMCID: PMC11187868 DOI: 10.1002/pro.5075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2024] [Revised: 05/24/2024] [Accepted: 05/27/2024] [Indexed: 06/21/2024]
Abstract
Rheostat positions, which can be substituted with various amino acids to tune protein function across a range of outcomes, are a developing area for advancing personalized medicine and bioengineering. Current methods cannot accurately predict which proteins contain rheostat positions or their substitution outcomes. To compare the prevalence of rheostat positions in homologs, we previously investigated their occurrence in two pyruvate kinase (PYK) isozymes. Human liver PYK contained numerous rheostat positions that tuned the apparent affinity for the substrate phosphoenolpyruvate (Kapp-PEP) across a wide range. In contrast, no functional rheostat positions were identified in Zymomonas mobilis PYK (ZmPYK). Further, the set of ZmPYK substitutions included an unusually large number that lacked measurable activity. We hypothesized that the inactive substitution variants had reduced protein stability, precluding detection of Kapp-PEP tuning. Using modified buffers, robust enzymatic activity was obtained for 19 previously-inactive ZmPYK substitution variants at three positions. Surprisingly, both previously-inactive and previously-active substitution variants all had Kapp-PEP values close to wild-type. Thus, none of the three positions were functional rheostat positions, and, unlike human liver PYK, ZmPYK's Kapp-PEP remained poorly tunable by single substitutions. To directly assess effects on stability, we performed thermal denaturation experiments for all ZmPYK substitution variants. Many diminished stability, two enhanced stability, and the three positions showed different thermal sensitivity to substitution, with one position acting as a "stability rheostat." The differences between the two PYK homologs raises interesting questions about the underlying mechanism(s) that permit functional tuning by single substitutions in some proteins but not in others.
Collapse
Affiliation(s)
- Pierce T. O'Neil
- Department of Biochemistry and Molecular BiologyThe University of Kansas Medical CenterKansasUSA
| | - Liskin Swint‐Kruse
- Department of Biochemistry and Molecular BiologyThe University of Kansas Medical CenterKansasUSA
| | - Aron W. Fenton
- Department of Biochemistry and Molecular BiologyThe University of Kansas Medical CenterKansasUSA
| |
Collapse
|
2
|
Swint-Kruse L, Fenton AW. Rheostats, toggles, and neutrals, Oh my! A new framework for understanding how amino acid changes modulate protein function. J Biol Chem 2024; 300:105736. [PMID: 38336297 PMCID: PMC10914490 DOI: 10.1016/j.jbc.2024.105736] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Revised: 01/09/2024] [Accepted: 01/25/2024] [Indexed: 02/12/2024] Open
Abstract
Advances in personalized medicine and protein engineering require accurately predicting outcomes of amino acid substitutions. Many algorithms correctly predict that evolutionarily-conserved positions show "toggle" substitution phenotypes, which is defined when a few substitutions at that position retain function. In contrast, predictions often fail for substitutions at the less-studied "rheostat" positions, which are defined when different amino acid substitutions at a position sample at least half of the possible functional range. This review describes efforts to understand the impact and significance of rheostat positions: (1) They have been observed in globular soluble, integral membrane, and intrinsically disordered proteins; within single proteins, their prevalence can be up to 40%. (2) Substitutions at rheostat positions can have biological consequences and ∼10% of substitutions gain function. (3) Although both rheostat and "neutral" (defined when all substitutions exhibit wild-type function) positions are nonconserved, the two classes have different evolutionary signatures. (4) Some rheostat positions have pleiotropic effects on function, simultaneously modulating multiple parameters (e.g., altering both affinity and allosteric coupling). (5) In structural studies, substitutions at rheostat positions appear to cause only local perturbations; the overall conformations appear unchanged. (6) Measured functional changes show promising correlations with predicted changes in protein dynamics; the emergent properties of predicted, dynamically coupled amino acid networks might explain some of the complex functional outcomes observed when substituting rheostat positions. Overall, rheostat positions provide unique opportunities for using single substitutions to tune protein function. Future studies of these positions will yield important insights into the protein sequence/function relationship.
Collapse
Affiliation(s)
- Liskin Swint-Kruse
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA.
| | - Aron W Fenton
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| |
Collapse
|
3
|
McCullagh M, Zeczycki TN, Kariyawasam CS, Durie CL, Halkidis K, Fitzkee NC, Holt JM, Fenton AW. What is allosteric regulation? Exploring the exceptions that prove the rule! J Biol Chem 2024; 300:105672. [PMID: 38272229 PMCID: PMC10897898 DOI: 10.1016/j.jbc.2024.105672] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2023] [Revised: 01/09/2024] [Accepted: 01/12/2024] [Indexed: 01/27/2024] Open
Abstract
"Allosteric" was first introduced to mean the other site (i.e., a site distinct from the active or orthosteric site), an adjective for "regulation" to imply a regulatory outcome resulting from ligand binding at another site. That original idea outlines a system with two ligand-binding events at two distinct locations on a macromolecule (originally a protein system), which defines a four-state energy cycle. An allosteric energy cycle provides a quantifiable allosteric coupling constant and focuses our attention on the unique properties of the four equilibrated protein complexes that constitute the energy cycle. Because many observed phenomena have been referenced as "allosteric regulation" in the literature, the goal of this work is to use literature examples to explore which systems are and are not consistent with the two-ligand thermodynamic energy cycle-based definition of allosteric regulation. We emphasize the need for consistent language so comparisons can be made among the ever-increasing number of allosteric systems. Building on the mutually exclusive natures of an energy cycle definition of allosteric regulation versus classic two-state models, we conclude our discussion by outlining how the often-proposed Rube-Goldberg-like mechanisms are likely inconsistent with an energy cycle definition of allosteric regulation.
Collapse
Affiliation(s)
- Martin McCullagh
- Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma, USA
| | - Tonya N Zeczycki
- Department of Biochemistry and Molecular Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina, USA
| | - Chathuri S Kariyawasam
- Department of Chemistry, Mississippi State University, Mississippi State, Mississippi, USA
| | - Clarissa L Durie
- Department of Biochemistry, University of Missouri, Columbia, Missouri, USA
| | - Konstantine Halkidis
- Department of Hematologic Malignancies and Cellular Therapeutics, The University of Kansas Medical Center, Kansas City, Kansas, USA; Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Nicholas C Fitzkee
- Department of Chemistry, Mississippi State University, Mississippi State, Mississippi, USA
| | - Jo M Holt
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Aron W Fenton
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA.
| |
Collapse
|
4
|
Sreenivasan S, Heffren P, Suh K, Rodnin MV, Kosa E, Fenton AW, Ladokhin AS, Smith PE, Fontes JD, Swint‐Kruse L. The intrinsically disordered transcriptional activation domain of CIITA is functionally tuneable by single substitutions: An exception or a new paradigm? Protein Sci 2024; 33:e4863. [PMID: 38073129 PMCID: PMC10806935 DOI: 10.1002/pro.4863] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Revised: 12/04/2023] [Accepted: 12/07/2023] [Indexed: 01/27/2024]
Abstract
During protein evolution, some amino acid substitutions modulate protein function ("tuneability"). In most proteins, the tuneable range is wide and can be sampled by a set of protein variants that each contains multiple amino acid substitutions. In other proteins, the full tuneable range can be accessed by a set of variants that each contains a single substitution. Indeed, in some globular proteins, the full tuneable range can be accessed by the set of site-saturating substitutions at an individual "rheostat" position. However, in proteins with intrinsically disordered regions (IDRs), most functional studies-which would also detect tuneability-used multiple substitutions or small deletions. In disordered transcriptional activation domains (ADs), studies with multiple substitutions led to the "acidic exposure" model, which does not anticipate the existence of rheostat positions. In the few studies that did assess effects of single substitutions on AD function, results were mixed: the ADs of two full-length transcription factors did not show tuneability, whereas a fragment of a third AD was tuneable by single substitutions. In this study, we tested tuneability in the AD of full-length human class II transactivator (CIITA). Sequence analyses and experiments showed that CIITA's AD is an IDR. Functional assays of singly-substituted AD variants showed that CIITA's function was highly tuneable, with outcomes not predicted by the acidic exposure model. Four tested positions showed rheostat behavior for transcriptional activation. Thus, tuneability of different IDRs can vary widely. Future studies are needed to illuminate the biophysical features that govern whether an IDR is tuneable by single substitutions.
Collapse
Affiliation(s)
- Shwetha Sreenivasan
- Department of Biochemistry and Molecular BiologyUniversity of Kansas Medical CenterKansas CityKansasUSA
| | - Paul Heffren
- Department of Biochemistry and Molecular BiologyUniversity of Kansas Medical CenterKansas CityKansasUSA
- Present address:
Department of BiosciencesKansas City UniversityKansas CityMissouriUSA
| | - Kyung‐Shin Suh
- Department of ChemistryKansas State UniversityManhattanKansasUSA
| | - Mykola V. Rodnin
- Department of Biochemistry and Molecular BiologyUniversity of Kansas Medical CenterKansas CityKansasUSA
| | - Edina Kosa
- Department of Biochemistry and Molecular BiologyUniversity of Kansas Medical CenterKansas CityKansasUSA
| | - Aron W. Fenton
- Department of Biochemistry and Molecular BiologyUniversity of Kansas Medical CenterKansas CityKansasUSA
| | - Alexey S. Ladokhin
- Department of Biochemistry and Molecular BiologyUniversity of Kansas Medical CenterKansas CityKansasUSA
| | - Paul E. Smith
- Department of ChemistryKansas State UniversityManhattanKansasUSA
| | - Joseph D. Fontes
- Department of Biochemistry and Molecular BiologyUniversity of Kansas Medical CenterKansas CityKansasUSA
| | - Liskin Swint‐Kruse
- Department of Biochemistry and Molecular BiologyUniversity of Kansas Medical CenterKansas CityKansasUSA
| |
Collapse
|
5
|
Shirvanizadeh N, Vihinen M. VariBench, new variation benchmark categories and data sets. FRONTIERS IN BIOINFORMATICS 2023; 3:1248732. [PMID: 37795169 PMCID: PMC10546188 DOI: 10.3389/fbinf.2023.1248732] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2023] [Accepted: 09/08/2023] [Indexed: 10/06/2023] Open
Affiliation(s)
| | - Mauno Vihinen
- Department of Experimental Medical Science, Lund University, Lund, Sweden
| |
Collapse
|
6
|
Meneely KM, McFarlane JS, Wright CL, Vela K, Swint-Kruse L, Fenton AW, Lamb AL. The 2.4 Å structure of Zymomonas mobilis pyruvate kinase: Implications for stability and regulation. Arch Biochem Biophys 2023; 744:109679. [PMID: 37393983 PMCID: PMC11257031 DOI: 10.1016/j.abb.2023.109679] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2023] [Revised: 06/27/2023] [Accepted: 06/28/2023] [Indexed: 07/04/2023]
Abstract
Human liver pyruvate kinase (hlPYK) catalyzes the final step in glycolysis, the formation of pyruvate (PYR) and ATP from phosphoenolpyruvate (PEP) and ADP. Fructose 1,6-bisphosphate (FBP), a pathway intermediate of glycolysis, serves as an allosteric activator of hlPYK. Zymomonas mobilis pyruvate kinase (ZmPYK) performs the final step of the Entner-Doudoroff pathway, which is similar to glycolysis in that energy is harvested from glucose and pyruvate is generated. The Entner-Doudoroff pathway does not have FBP as a pathway intermediate, and ZmPYK is not allosterically activated. In this work, we solved the 2.4 Å X-ray crystallographic structure of ZmPYK. The protein is dimeric in solution as determined by gel filtration chromatography, but crystallizes as a tetramer. The buried surface area of the ZmPYK tetramerization interface is significantly smaller than that of hlPYK, and yet tetramerization using the standard interfaces from higher organisms provides an accessible low energy crystallization pathway. Interestingly, the ZmPYK structure showed a phosphate ion in the analogous location to the 6-phosphate binding site of FBP in hlPYK. Circular Dichroism (CD) was used to measure melting temperatures of hlPYK and ZmPYK in the absence and presence of substrates and effectors. The only significant difference was an additional phase of small amplitude for the ZmPYK melting curves. We conclude that the phosphate ion plays neither a structural or allosteric role in ZmPYK under the conditions tested. We hypothesize that ZmPYK does not have sufficient protein stability for activity to be tuned by allosteric effectors as described for rheostat positions in the allosteric homologues.
Collapse
Affiliation(s)
- Kathleen M Meneely
- Department of Chemistry, University of Texas at San Antonio, San Antonio, TX, 78249, USA
| | - Jeffrey S McFarlane
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS, 66045, USA
| | - Collette L Wright
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS, 66045, USA
| | - Kathryn Vela
- Department of Chemistry, University of Texas at San Antonio, San Antonio, TX, 78249, USA
| | - Liskin Swint-Kruse
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS, 66160, USA
| | - Aron W Fenton
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS, 66160, USA
| | - Audrey L Lamb
- Department of Chemistry, University of Texas at San Antonio, San Antonio, TX, 78249, USA.
| |
Collapse
|
7
|
Swint-Kruse L, Dougherty LL, Page B, Wu T, O’Neil PT, Prasannan CB, Timmons C, Tang Q, Parente DJ, Sreenivasan S, Holyoak T, Fenton AW. PYK-SubstitutionOME: an integrated database containing allosteric coupling, ligand affinity and mutational, structural, pathological, bioinformatic and computational information about pyruvate kinase isozymes. Database (Oxford) 2023; 2023:baad030. [PMID: 37171062 PMCID: PMC10176505 DOI: 10.1093/database/baad030] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2022] [Revised: 03/29/2023] [Accepted: 04/11/2023] [Indexed: 05/13/2023]
Abstract
Interpreting changes in patient genomes, understanding how viruses evolve and engineering novel protein function all depend on accurately predicting the functional outcomes that arise from amino acid substitutions. To that end, the development of first-generation prediction algorithms was guided by historic experimental datasets. However, these datasets were heavily biased toward substitutions at positions that have not changed much throughout evolution (i.e. conserved). Although newer datasets include substitutions at positions that span a range of evolutionary conservation scores, these data are largely derived from assays that agglomerate multiple aspects of function. To facilitate predictions from the foundational chemical properties of proteins, large substitution databases with biochemical characterizations of function are needed. We report here a database derived from mutational, biochemical, bioinformatic, structural, pathological and computational studies of a highly studied protein family-pyruvate kinase (PYK). A centerpiece of this database is the biochemical characterization-including quantitative evaluation of allosteric regulation-of the changes that accompany substitutions at positions that sample the full conservation range observed in the PYK family. We have used these data to facilitate critical advances in the foundational studies of allosteric regulation and protein evolution and as rigorous benchmarks for testing protein predictions. We trust that the collected dataset will be useful for the broader scientific community in the further development of prediction algorithms. Database URL https://github.com/djparente/PYK-DB.
Collapse
Affiliation(s)
- Liskin Swint-Kruse
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160, USA
| | - Larissa L Dougherty
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160, USA
| | - Braelyn Page
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160, USA
| | - Tiffany Wu
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160, USA
| | - Pierce T O’Neil
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160, USA
| | - Charulata B Prasannan
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160, USA
| | - Cody Timmons
- Chemistry Department, Southwestern Oklahoma State University, 100 Campus Dr., Weatherford, OK 73096, USA
| | - Qingling Tang
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160, USA
| | - Daniel J Parente
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160, USA
- Department of Family Medicine and Community Health, The University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160, USA
| | - Shwetha Sreenivasan
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160, USA
| | - Todd Holyoak
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160, USA
- Department of Biology, University of Waterloo, 200 University Ave. W, Waterloo, ON N2L 3G1, Canada
| | - Aron W Fenton
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160, USA
| |
Collapse
|
8
|
Page BM, Martin TA, Wright CL, Fenton LA, Villar MT, Tang Q, Artigues A, Lamb A, Fenton AW, Swint-Kruse L. Odd one out? Functional tuning of Zymomonas mobilis pyruvate kinase is narrower than its allosteric, human counterpart. Protein Sci 2022; 31:e4336. [PMID: 35762709 DOI: 10.1002/pro.4336] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2022] [Revised: 04/29/2022] [Accepted: 05/03/2022] [Indexed: 11/08/2022]
Abstract
Various protein properties are often illuminated using sequence comparisons of protein homologs. For example, in analyses of the pyruvate kinase multiple sequence alignment, the set of positions that changed during speciation ("phylogenetic" positions) were enriched for "rheostat" positions in human liver pyruvate kinase (hLPYK). (Rheostat positions are those which, when substituted with various amino acids, yield a range of functional outcomes). However, the correlation was moderate, which could result from multiple biophysical constraints acting on the same position during evolution and/or various sources of noise. To further examine this correlation, we here tested Zymomonas mobilis PYK (ZmPYK), which has <65% sequence identity to any other PYK sequence. Twenty-six ZmPYK positions were selected based on their phylogenetic scores, substituted with multiple amino acids, and assessed for changes in Kapp-PEP . Although we expected to identify multiple, strong rheostat positions, only one moderate rheostat position was detected. Instead, nearly half of the 271 ZmPYK variants were inactive and most others showed near wild-type function. Indeed, for the active ZmPYK variants, the total range of Kapp,PEP values ("tunability") was 40-fold less than that observed for hLPYK variants. The combined functional studies and sequence comparisons suggest that ZmPYK has evolved functional and/or structural attributes that differ from the rest of the family. We hypothesize that including such "orphan" sequences in MSA analyses obscures the correlations used to predict rheostat positions. Finally, results raise the intriguing biophysical question as to how the same protein fold can support rheostat positions in one homolog but not another.
Collapse
Affiliation(s)
- Braelyn M Page
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Tyler A Martin
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Collette L Wright
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA.,Department of Molecular Biosciences, The University of Kansas, Lawrence, Kansas, USA
| | - Lauren A Fenton
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Maite T Villar
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Qingling Tang
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Antonio Artigues
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Audrey Lamb
- Department of Molecular Biosciences, The University of Kansas, Lawrence, Kansas, USA.,Department of Chemistry, University of Texas at San Antonio, San Antonio, Texas, USA
| | - Aron W Fenton
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Liskin Swint-Kruse
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| |
Collapse
|
9
|
Ruggiero MJ, Malhotra S, Fenton AW, Swint-Kruse L, Karanicolas J, Hagenbuch B. Structural Plasticity Is a Feature of Rheostat Positions in the Human Na +/Taurocholate Cotransporting Polypeptide (NTCP). Int J Mol Sci 2022; 23:ijms23063211. [PMID: 35328632 PMCID: PMC8954283 DOI: 10.3390/ijms23063211] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 03/11/2022] [Accepted: 03/15/2022] [Indexed: 02/05/2023] Open
Abstract
In the Na+/taurocholate cotransporting polypeptide (NTCP), the clinically relevant S267F polymorphism occurs at a "rheostat position". That is, amino acid substitutions at this position ("S267X") lead to a wide range of functional outcomes. This result was particularly striking because molecular models predicted the S267X side chains are buried, and thus, usually expected to be less tolerant of substitutions. To assess whether structural tolerance to buried substitutions is widespread in NTCP, here we used Rosetta to model all 19 potential substitutions at another 13 buried positions. Again, only subtle changes in the calculated stabilities and structures were predicted. Calculations were experimentally validated for 19 variants at codon 271 ("N271X"). Results showed near wildtype expression and rheostatic modulation of substrate transport, implicating N271 as a rheostat position. Notably, each N271X substitution showed a similar effect on the transport of three different substrates and thus did not alter substrate specificity. This differs from S267X, which altered both transport kinetics and specificity. As both transport and specificity may change during protein evolution, the recognition of such rheostat positions may be important for evolutionary studies. We further propose that the presence of rheostat positions is facilitated by local plasticity within the protein structure. Finally, we note that identifying rheostat positions may advance efforts to predict new biomedically relevant missense variants in NTCP and other membrane transport proteins.
Collapse
Affiliation(s)
- Melissa J. Ruggiero
- Department of Pharmacology, Toxicology and Therapeutics, The University of Kansas Medical Center, Kansas City, KS 66160, USA;
| | - Shipra Malhotra
- Program in Molecular Therapeutics, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA; (S.M.); (J.K.)
| | - Aron W. Fenton
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, KS 66160, USA; (A.W.F.); (L.S.-K.)
| | - Liskin Swint-Kruse
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, KS 66160, USA; (A.W.F.); (L.S.-K.)
| | - John Karanicolas
- Program in Molecular Therapeutics, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA; (S.M.); (J.K.)
| | - Bruno Hagenbuch
- Department of Pharmacology, Toxicology and Therapeutics, The University of Kansas Medical Center, Kansas City, KS 66160, USA;
- Correspondence:
| |
Collapse
|
10
|
Fenton KD, Meneely KM, Wu T, Martin TA, Swint‐Kruse L, Fenton AW, Lamb AL. Substitutions at a rheostat position in human aldolase A cause a shift in the conformational population. Protein Sci 2022; 31:357-370. [PMID: 34734672 PMCID: PMC8819835 DOI: 10.1002/pro.4222] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2021] [Revised: 10/28/2021] [Accepted: 10/28/2021] [Indexed: 02/03/2023]
Abstract
Some protein positions play special roles in determining the magnitude of protein function: at such "rheostat" positions, varied amino acid substitutions give rise to a continuum of functional outcomes, from wild type (or enhanced), to intermediate, to loss of function. This observed range raises interesting questions about the biophysical bases by which changes at single positions have such varied outcomes. Here, we assessed variants at position 98 in human aldolase A ("I98X"). Despite being ~17 Å from the active site and far from subunit interfaces, substitutions at position 98 have rheostatic contributions to the apparent cooperativity (nH ) associated with fructose-1,6-bisphosphate substrate binding and moderately affected binding affinity. Next, we crystallized representative I98X variants to assess structural consequences. Residues smaller than the native isoleucine (cysteine and serine) were readily accommodated, and the larger phenylalanine caused only a slight separation of the two parallel helixes. However, the diffraction quality was reduced for I98F, and further reduced for I98Y. Intriguingly, the resolutions of the I98X structures correlated with their nH values. We propose that substitution effects on both nH and crystal lattice disruption arise from changes in the population of aldolase A conformations in solution. In combination with results computed for rheostat positions in other proteins, the results from this study suggest that rheostat positions accommodate a wide range of side chains and that structural consequences manifest as shifted ensemble populations and/or dynamics changes.
Collapse
Affiliation(s)
- Kathryn D. Fenton
- Department of Biochemistry and Molecular BiologyThe University of Kansas Medical CenterKansas CityKansasUSA
| | - Kathleen M. Meneely
- Department of ChemistryUniversity of Texas at San AntonioSan AntonioTexasUSA
| | - Tiffany Wu
- Department of Biochemistry and Molecular BiologyThe University of Kansas Medical CenterKansas CityKansasUSA
| | - Tyler A. Martin
- Department of Biochemistry and Molecular BiologyThe University of Kansas Medical CenterKansas CityKansasUSA
| | - Liskin Swint‐Kruse
- Department of Biochemistry and Molecular BiologyThe University of Kansas Medical CenterKansas CityKansasUSA
| | - Aron W. Fenton
- Department of Biochemistry and Molecular BiologyThe University of Kansas Medical CenterKansas CityKansasUSA
| | - Audrey L. Lamb
- Department of ChemistryUniversity of Texas at San AntonioSan AntonioTexasUSA
| |
Collapse
|
11
|
Campitelli P, Swint-Kruse L, Ozkan SB. Substitutions at Nonconserved Rheostat Positions Modulate Function by Rewiring Long-Range, Dynamic Interactions. Mol Biol Evol 2021; 38:201-214. [PMID: 32780837 PMCID: PMC7783170 DOI: 10.1093/molbev/msaa202] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Amino acid substitutions at nonconserved protein positions can have noncanonical and "long-distance" outcomes on protein function. Such outcomes might arise from changes in the internal protein communication network, which is often accompanied by changes in structural flexibility. To test this, we calculated flexibilities and dynamic coupling for positions in the linker region of the lactose repressor protein. This region contains nonconserved positions for which substitutions alter DNA-binding affinity. We first chose to study 11 substitutions at position 52. In computations, substitutions showed long-range effects on flexibilities of DNA-binding positions, and the degree of flexibility change correlated with experimentally measured changes in DNA binding. Substitutions also altered dynamic coupling to DNA-binding positions in a manner that captured other experimentally determined functional changes. Next, we broadened calculations to consider the dynamic coupling between 17 linker positions and the DNA-binding domain. Experimentally, these linker positions exhibited a wide range of substitution outcomes: Four conserved positions tolerated hardly any substitutions ("toggle"), ten nonconserved positions showed progressive changes from a range of substitutions ("rheostat"), and three nonconserved positions tolerated almost all substitutions ("neutral"). In computations with wild-type lactose repressor protein, the dynamic couplings between the DNA-binding domain and these linker positions showed varied degrees of asymmetry that correlated with the observed toggle/rheostat/neutral substitution outcomes. Thus, we propose that long-range and noncanonical substitutions outcomes at nonconserved positions arise from rewiring long-range communication among functionally important positions. Such calculations might enable predictions for substitution outcomes at a range of nonconserved positions.
Collapse
Affiliation(s)
- Paul Campitelli
- Department of Physics, Center for Biological Physics, Arizona State University, Tempe, AZ
| | - Liskin Swint-Kruse
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, KS
| | - S Banu Ozkan
- Department of Physics, Center for Biological Physics, Arizona State University, Tempe, AZ
| |
Collapse
|
12
|
Swint-Kruse L, Martin TA, Page BM, Wu T, Gerhart PM, Dougherty LL, Tang Q, Parente DJ, Mosier BR, Bantis LE, Fenton AW. Rheostat functional outcomes occur when substitutions are introduced at nonconserved positions that diverge with speciation. Protein Sci 2021; 30:1833-1853. [PMID: 34076313 DOI: 10.1002/pro.4136] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Revised: 05/25/2021] [Accepted: 05/28/2021] [Indexed: 12/14/2022]
Abstract
When amino acids vary during evolution, the outcome can be functionally neutral or biologically-important. We previously found that substituting a subset of nonconserved positions, "rheostat" positions, can have surprising effects on protein function. Since changes at rheostat positions can facilitate functional evolution or cause disease, more examples are needed to understand their unique biophysical characteristics. Here, we explored whether "phylogenetic" patterns of change in multiple sequence alignments (such as positions with subfamily specific conservation) predict the locations of functional rheostat positions. To that end, we experimentally tested eight phylogenetic positions in human liver pyruvate kinase (hLPYK), using 10-15 substitutions per position and biochemical assays that yielded five functional parameters. Five positions were strongly rheostatic and three were non-neutral. To test the corollary that positions with low phylogenetic scores were not rheostat positions, we combined these phylogenetic positions with previously-identified hLPYK rheostat, "toggle" (most substitution abolished function), and "neutral" (all substitutions were like wild-type) positions. Despite representing 428 variants, this set of 33 positions was poorly statistically powered. Thus, we turned to the in vivo phenotypic dataset for E. coli lactose repressor protein (LacI), which comprised 12-13 substitutions at 329 positions and could be used to identify rheostat, toggle, and neutral positions. Combined hLPYK and LacI results show that positions with strong phylogenetic patterns of change are more likely to exhibit rheostat substitution outcomes than neutral or toggle outcomes. Furthermore, phylogenetic patterns were more successful at identifying rheostat positions than were co-evolutionary or eigenvector centrality measures of evolutionary change.
Collapse
Affiliation(s)
- Liskin Swint-Kruse
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Tyler A Martin
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Braelyn M Page
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Tiffany Wu
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Paige M Gerhart
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Larissa L Dougherty
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA.,Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth College, Hanover, New Hampshire, USA
| | - Qingling Tang
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Daniel J Parente
- Department of Family Medicine and Community Health, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Brian R Mosier
- Department of Biostatistics and Data Science, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Leonidas E Bantis
- Department of Biostatistics and Data Science, The University of Kansas Medical Center, Kansas City, Kansas, USA
| | - Aron W Fenton
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas, USA
| |
Collapse
|
13
|
Abstract
To achieve the full potential of pharmacogenomics, one must accurately predict the functional outcomes that arise from amino acid substitutions in proteins. Classically, researchers have focused on understanding the consequences of individual substitutions. However, literature surveys have shown that most substitutions were created at evolutionarily conserved positions. Awareness of this bias leads to a shift in perspective, from considering the outcomes of individual substitutions to understanding the roles of individual protein positions. Conserved positions tend to act as “toggle” switches, with most substitutions abolishing function. However, nonconserved positions have been found equally capable of affecting protein function. Indeed, many nonconserved positions act like functional dimmer switches (“rheostat” positions): this is revealed when multiple substitutions are made at a single position. Each substitution has a different functional outcome; the set of substitutions spans a range of outcomes. Finally, some nonconserved positions appear neutral, capable of accommodating all amino acid types without modifying function. This paper reviews the currently-known properties of rheostat positions, with examples shown for pyruvate kinase, organic anion transporting polypeptide 1B1, the beta-lactamase inhibitory protein, and angiotensin-converting enzyme 2. Outcomes observed for rheostat positions have implications for the rational design of drug analogs and allosteric drugs. Furthermore, this new framework—comprising three types of protein positions—provides a new approach to interpreting disease and population-based databases of amino acid changes. In conclusion, although a full understanding of substitution outcomes at rheostat positions poses a challenge, utilization of this new frame of reference will further advance the application of pharmacogenomics.
Collapse
|