Abstract
The structures of a cyanophage small heat shock protein (sHSP) were determined as octahedrons of 24-mers and 48-mers and as icosahedrons of 60-mers. An N-terminal deletion construct of an 18 kDa sHSP of Synechococcus sp. phage S-ShM2 crystallized as a 24-mer and its structure was determined at a resolution of 7 Å. The negative stain electron microscopy (EM) images showed that the full-length protein is a mixture of a major population of larger and a minor population of smaller cage-like particles. Their structures have been determined by electron cryomicroscopy 3D image reconstruction at a resolution of 8 Å. The larger particles are 60-mers with icosahedral symmetry and the smaller ones are 48-mers with octahedral symmetry. These structures are the first of the viral/phage origin and the 60-mer is the largest and the first icosahedral assembly to be reported for sHSPs.
Highlights
The structures of a cyanophage small heat shock protein were determined as octahedrons of 24-mers and 48-mers and as icosahedrons of 60-mers
The oligomer sizes were determined by SEC–MALS (Fig. 2A) and their polydispersity was measured by dynamic light scattering (DLS) (Fig. 2B)
We present the structural features of SM2 constructs and compare them with other available structures of this class of proteins
Summary
The structures of a cyanophage small heat shock protein (sHSP) were determined as octahedrons of 24-mers and 48-mers and as icosahedrons of 60-mers. The larger particles are 60-mers with icosahedral symmetry and the smaller ones are 48-mers with octahedral symmetry These structures are the first of the viral/phage origin and the 60-mer is the largest and the first icosahedral assembly to be reported for sHSPs. Small heat shock proteins (sHSPs) prevent the aggregation of cellular proteins during heat and other types of stress. Small heat shock proteins (sHSPs) prevent the aggregation of cellular proteins during heat and other types of stress They exist in dynamic equilibrium by the constant exchange of subunits between oligomers of various sizes. SHSPs are the front line of defence against the detrimental effects of cellular protein unfolding They bind to a large variety of non-native proteins ranging from peptides to large p roteins[4] and efficiently prevent irreversible aggregation processes. Cryo-EM analysis revealed that T4 lysozyme is located inside the cage-like structures of the 24-mers and 48-mers of Methanocaldococcus jannaschii HSP16.5 interacting with the N-termini[22]
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