Abstract
Group II chaperonins found in archaea and in eukaryotic cytosol mediate protein folding without a GroES-like cofactor. The function of the cofactor is substituted by the helical protrusion at the tip of the apical domain, which forms a built-in lid on the central cavity. Although many studies on the change in lid conformation coupled to the binding and hydrolysis of nucleotides have been conducted, the molecular mechanism of lid closure remains poorly understood. Here, we performed a single-molecule polarization modulation to probe the rotation of the helical protrusion of a chaperonin from a hyperthermophilic archaeum, Thermococcus sp. strain KS-1. We detected approximately 35° rotation of the helical protrusion immediately after photorelease of ATP. The result suggests that the conformational change from the open lid to the closed lid state is responsible for the approximately 35° rotation of the helical protrusion.
Highlights
Chaperonins are ubiquitous molecular chaperones that form double-ring assemblies of about 60 kDa subunits
There are two phylogenic groups of chaperonins [3,4]: Group I chaperonins, which are present in bacteria (GroEL), mitochondria, chloroplasts (Rubisco subunit binding protein, RBP), and some archaea, consist of double heptameric rings; Group II chaperonins, which are present in archaea and the eukaryotic cytosol [known as TCP1 ring complex (TRiC) or chaperonin-containing TCP1 (CCT)] are assembled in two octameric or nonameric rings
We demonstrated that the conformational change from an open lid to closed lid state can be achieved by approximately 35u rotation of the helical protrusion
Summary
Chaperonins are ubiquitous molecular chaperones that form double-ring assemblies of about 60 kDa subunits. There are two phylogenic groups of chaperonins [3,4]: Group I chaperonins, which are present in bacteria (GroEL), mitochondria (mitochondrial 60-kDa heat-shock protein, mtHsp60), chloroplasts (Rubisco subunit binding protein, RBP), and some archaea, consist of double heptameric rings; Group II chaperonins, which are present in archaea (referred to as thermosomes) and the eukaryotic cytosol [known as TCP1 ring complex (TRiC) or chaperonin-containing TCP1 (CCT)] are assembled in two octameric or nonameric rings. Each subunit comprises three distinct domains: equatorial, intermediate, and apical (Figure 1A). The equatorial domain contains the ATP binding site and is involved in intra- and inter-ring contacts. The apical domain is involved in binding to substrate proteins. The intermediate domain connects the equatorial and apical domains of each subunit, and transfers the ATP-induced conformational changes from the equatorial to the apical domain
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