title: The Chaperone Activity and Substrate Spectrum of Human Small Heat Shock Proteins.
abstract: Small heat shock proteins (sHsps) are a ubiquitous family of molecular chaperones that suppress the unspecific aggregation of miscellaneous proteins. Multicellular organisms contain a large number of different sHsps, raising questions as to whether they function redundantly or are specialized in terms of substrates and mechanism. To gain insight into this issue, we undertook a comparative analysis of the eight major human sHsps on the aggregation of both model proteins and cytosolic lysates under standardized conditions. We discovered that sHsps, which form large oligomers (HspB1/Hsp27, HspB3, HspB4/αA-crystallin, and HspB5/αB-crystallin) are promiscuous chaperones, whereas the chaperone activity of the other sHsps is more substrate-dependent. However, all human sHsps analyzed except HspB7 suppressed the aggregation of cytosolic proteins of HEK293 cells. We identified ∼1100 heat-sensitive HEK293 proteins, 12% of which could be isolated in complexes with sHsps. Analysis of their biochemical properties revealed that most of the sHsp substrates have a molecular mass from 50 to 100 kDa and a slightly acidic pI (5.4-6.8). The potency of the sHsps to suppress aggregation of model substrates is correlated with their ability to form stable substrate complexes; especially HspB1 and HspB5, but also B3, bind tightly to a variety of proteins, whereas fewer substrates were detected in complex with the other sHsps, although these were also efficient in preventing the aggregation of cytosolic proteins.
authors.affiliation: From the Center for Integrated Protein Science at the Department Chemie, Technische Universität München, Lichtenbergstrasse 4, 85748 Garching, Germany.
authors.forename: Evgeny V
authors.initials: EV
authors.lastname: Mymrikov
authors.affiliation: From the Center for Integrated Protein Science at the Department Chemie, Technische Universität München, Lichtenbergstrasse 4, 85748 Garching, Germany.
authors.forename: Marina
authors.initials: M
authors.lastname: Daake
authors.affiliation: From the Center for Integrated Protein Science at the Department Chemie, Technische Universität München, Lichtenbergstrasse 4, 85748 Garching, Germany.
authors.forename: Bettina
authors.initials: B
authors.lastname: Richter
authors.affiliation: From the Center for Integrated Protein Science at the Department Chemie, Technische Universität München, Lichtenbergstrasse 4, 85748 Garching, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Haslbeck
authors.affiliation: From the Center for Integrated Protein Science at the Department Chemie, Technische Universität München, Lichtenbergstrasse 4, 85748 Garching, Germany johannes.buchner@tum.de.
authors.forename: Johannes
authors.initials: J
authors.lastname: Buchner
mesh_terms: D057809:HEK293 Cells; D055551:HSP27 Heat-Shock Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D011485:Protein Binding; D013379:Substrate Specificity / Q000502:physiology
chemical_list: D055551:HSP27 Heat-Shock Proteins
keywords: cataract; molecular chaperone; protein aggregation; protein stability; small heat shock protein (sHsp); substrate proteins; α crystallin