Two Bacterial Small Heat Shock Proteins, IbpA and IbpB, Form a Functional Heterodimer. Issue 15 (23rd July 2021)

• Record Type: Journal Article
• Authors: Piróg, Artur; Cantini, Francesca; Nierzwicki, Łukasz; Obuchowski, Igor; Tomiczek, Bartłomiej; Czub, Jacek; Liberek, Krzysztof
• Is Part Of: Journal of molecular biology. Volume 433:Issue 15(2021)
• Publication Date: 2021-07-23
• Subjects: bacterial small heat shock proteins -- chaperones -- modification of protein aggregation -- protein refolding -- heterodimer of sHsps; Molecular biology -- Periodicals; Biology -- Periodicals; Biochemistry -- Periodicals; Bacteriology -- Periodicals; Molecular Biology -- Periodicals; Biochemistry -- Periodicals; Biologie moléculaire -- Périodiques; Biologie -- Périodiques; Biochimie -- Périodiques; Moleculaire biologie; Biochemistry; Biology; Molecular biology; Periodicals; 572.805
• DOI: 10.1016/j.jmb.2021.167054
• Languages: English
• ISSNs: 0022-2836

Abstract

Graphical abstract: Highlights: Bacterial sHsps, IbpA and IbpB, cooperate in interaction with denatured substrates. Isolated IbpA and IbpB α-crystallin domains form a heterodimer. IbpA-IbpB heterodimer is a functional form of bacterial sHsps system. Abstract: Small heat shock proteins (sHsps) are a conserved class of ATP-independent chaperones which in stress conditions bind to unfolded protein substrates and prevent their irreversible aggregation. Substrates trapped in sHsps-containing aggregates are efficiently refolded into native structures by ATP-dependent Hsp70 and Hsp100 chaperones. Most γ-proteobacteria possess a single sHsp (IbpA), while in a subset of Enterobacterales, as a consequence of ibpA gene duplication event, a two-protein sHsp (IbpA and IbpB) system has evolved. IbpA and IbpB are functionally divergent. Purified IbpA, but not IbpB, stably interacts with aggregated substrates, yet both sHsps are required to be present at the substrate denaturation step for subsequent efficient Hsp70-Hsp100-dependent substrate refolding. IbpA and IbpB interact with each other, influence each other's expression levels and degradation rates. However, the crucial information on how these two sHsps interact and what is the basic building block required for proper sHsps functioning was missing. Here, based on NMR, mass spectrometry and crosslinking studies, we show that IbpA-IbpB heterodimer is a dominating functional unit of the two sHsp system in Enterobacterales . The principle of heterodimer formation is similar to one described for homodimers of single bacterial sHsps. β-hairpins formed by strands β5 and β7 of IbpA or IbpB crystallin domains associate with the other one's β-sandwich in the heterodimer structure. Relying on crosslinking and molecular dynamics studies, we also propose the orientation of two IbpA-IbpB heterodimers in a higher order tetrameric structure.