Allosteric Inter-Domain Contacts in Bacterial Hsp70 Are Located in Regions That Avoid Insertion and Deletion Events

Heat shock proteins 70 (Hsp70) are chaperones consisting of a nucleotide-binding domain (NBD) and a substrate-binding domain (SBD), the latter of which binds protein clients. After ATP binds to the NBD, the SBD α/β subdomains' shared interface opens, and the open SBD docks to the NBD. Such allosteric effects are stabilized by the newly formed NBD-SBD interdomain contacts. In this paper, we examined how such an opening and formation of subdomain interfaces is affected during the evolution of Hsp70. In particular, insertion and deletion events (indels) can be highly disruptive for the mechanical events since such changes introduce a collective shift in the pairing interactions at communicating interfaces. Based on a multiple sequence alignment analysis of data collected from Swiss-Prot/UniProt database, we find several indel-free regions (IFR) in Hsp70. The two largest IFRs are located in interdomain regions that participate in allosteric structural changes. We speculate that the reason why the indels have a lower likelihood of occurrence in these regions is that indel events in these regions cause dysfunction in the protein due to perturbations of the mechanical balance. Thus, the development of functional allosteric machines requires including in the rational design a concept of the balance between structural elements.