Latent Effects of Hsp90 Mutants Revealed at Reduced Expression Levels

By Li Jiang, Parul Mishra, Ryan T. Hietpas, Konstantin B. Zeldovich, Daniel N. A. Bolon. 2013

92 citations recorded by the source corpus.

In natural systems, selection acts on both protein sequence and expression level, but it is unclear how selection integrates over these two dimensions. We recently developed the EMPIRIC approach to systematically determine the fitness effects of all possible point mutants for important regions of essential genes in yeast. Here, we systematically investigated the fitness effects of point mutations in a putative substrate binding loop of yeast Hsp90 (Hsp82) over a broad range of expression strengths. Negative epistasis between reduced expression strength and amino acid substitutions was common, and the endogenous expression strength frequently obscured mutant defects. By analyzing fitness effects at varied expression strengths, we were able to uncover all mutant effects on function. The majority of mutants caused partial functional defects, consistent with this region of Hsp90 contributing to a mutation sensitive and critical process. These results demonstrate that important functional regions of proteins can tolerate mutational defects without experimentally observable impacts on fitness.

Subfields: Genetics, Molecular Biology

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Citations in the corpus

Merging molecular mechanism and evolution: theory and computation at the interface of biophysics and evolutionary population genetics (2014, background): “An alternative approach is ‘bottom up’ where genetic variation is introduced either rationally by genomic editing [10 ,74] or via targeted random or saturating mutagenesis [75 ,76] with subsequent analysis of fitness changes.”
Systematic exploration of ubiquitin sequence, E1 activation efficiency, and experimental fitness in yeast (2014, background): “While a wealth of studies demonstrate that the fitness effects of mutations are mediated by biochemical changes 19; 20; 21; 22; 23; 24; 25 , most systematic studies of mutants have focused predominantly on either growth effects 14; 26; 27 or biochemical effects 11; 28; 29; 30 .”
Systematic Mutant Analyses Elucidate General and Client-Specific Aspects of Hsp90 Function. (2016, methodology): “The effects of Hsp90 mutations on yeast growth rate were quantified based on changes in the frequency of each mutation during competitions where yeast growth rates are tightly coupled to the function of Hsp90 mutant variants by limiting the promoter strength driving their expression (Jiang et al., 2”
Quantifying and understanding the fitness effects of protein mutations: Laboratory versus nature (2016, background): “However, a potential disadvantage of measuring the effects of single mutations is the buffering of mildly deleterious effects(13)—a tendency that is further intensified when the protein under study is expressed at high levels.(12) The manner of calculating the fitness effects also varies between exp”
Systematic Mapping of Protein Mutational Space by Prolonged Drift Reveals the Deleterious Effects of Seemingly Neutral Mutations (2015, background): “However, at lower expression levels, these mutations did reveal deleterious fitness effects, thus indicating that the sensitivity of the experimental system is a key parameter [48].”