Concurrent action of purifying selection and gene conversion results in extreme conservation of the major stress-inducible Hsp70 genes in mammals

Abstract

Several evolutionary mechanisms alter the fate of mutations and genes within populations based on their exhibited functional effects. To understand the underlying mechanisms involved in the evolution of the cellular stress response, a very conserved mechanism in the course of organismal evolution, we studied the patterns of natural genetic variation and functional consequences of polymorphisms of two stress-inducible Hsp70 genes. These genes, HSPA1A and HSPA1B, are major orchestrators of the cellular stress response and are associated with several human diseases. Our phylogenetic analyses revealed that the duplication of HSPA1A and HSPA1B originated in a lineage proceeding to placental mammals, and henceforth they remained in conserved synteny. Additionally, analyses of synonymous and non-synonymous changes suggest that purifying selection shaped the HSPA1 gene diversification, while gene conversion resulted in high sequence conservation within species. In the human HSPA1-cluster, the vast majority of mutations are synonymous and specific genic regions are devoid of mutations. Furthermore, functional characterization of several human polymorphisms revealed subtle differences in HSPA1A stability and intracellular localization. Collectively, the observable patterns of HSPA1A-1B variation describe an evolutionary pattern, in which purifying selection and gene conversion act simultaneously and conserve a major orchestrator of the cellular stress response.

Functional characterization of natural variants found on the major stress inducible 70-kDa heat shock gene, HSPA1A, in humans

“…The mutations used in the present study (S16P, S16Y, R36C, I74T, I480N, F592S, and K71A as control) are described in detail in [3]. Their position was mapped onto the 3D model using PyMol (DeLano Scientific).…”

“…Loss of function or overexpression of HSPA1A, the major stress-inducible gene in humans, have been linked with heart, Alzheimer’s, and Parkinson’s diseases, as well as cancer [2]. However, the exact relationship between naturally occurring mutations and their outcome on the function of HSPA1A remains mostly uncharacterized [3]. …”

“…We identified and collected these mutations from the 1000 Genome project [1], and preliminarily characterized their evolution [3]. This initial characterization determined that these mutations have a very low frequency in humans and none of them alters an amino acid of known function [3].…”

“…We identified and collected these mutations from the 1000 Genome project [1], and preliminarily characterized their evolution [3]. This initial characterization determined that these mutations have a very low frequency in humans and none of them alters an amino acid of known function [3]. Furthermore, these analyses revealed that these mutations have subtle effects on protein stability, nucleotide binding, and protein subcellular localization and translocation after heat-shock [3].…”

“…This initial characterization determined that these mutations have a very low frequency in humans and none of them alters an amino acid of known function [3]. Furthermore, these analyses revealed that these mutations have subtle effects on protein stability, nucleotide binding, and protein subcellular localization and translocation after heat-shock [3]. However, based on the conservation, radicality, and structural position (Fig.…”