Multiple Functional Roles of the Accessory I-Domain of Bacteriophage P22 Coat Protein Revealed by NMR Structure and CryoEM Modeling
Publication date: Available online 15 May 2014
Source:Structure
Author(s): Alessandro*A. Rizzo , Margaret*M. Suhanovsky , Matthew*L. Baker , LaTasha*C.R. Fraser , Lisa*M. Jones , Don*L. Rempel , Michael*L. Gross , Wah Chiu , Andrei*T. Alexandrescu , Carolyn*M. Teschke
Some capsid proteins built on the ubiquitous HK97-fold have accessory domains imparting specific functions. Bacteriophage P22 coat protein has a unique insertion domain (I-domain). Two prior I-domain models from subnanometer cryoelectron microscopy (cryoEM) reconstructions differed substantially. Therefore, the I-domain’s nuclear magnetic resonance structure was determined and also used to improve cryoEM models of coat protein. The I-domain has an antiparallel six-stranded ?-barrel*fold, not previously observed in HK97-fold accessory domains. The D-loop, which is dynamic in the isolated I-domain and intact monomeric coat protein, forms stabilizing salt bridges between adjacent capsomers in procapsids. The S-loop is important for capsid size determination, likely through intrasubunit interactions. Ten of 18 coat protein temperature-sensitive-folding substitutions are in the I-domain, indicating its importance in folding and stability. Several are found on a positively charged face of the ?-barrel that anchors the I-domain to a negatively charged surface of the coat protein HK97-core.
Graphical abstract
Teaser
Bacteriophage P22 coat protein has a unique inserted I-domain. Rizzo et*al. determine an NMR structure of the I-domain and use it to improve cryoEM models of coat protein. The I-domain structure illuminates the function of the domain in the folding of coat protein as well as assembly and stability of procapsids.
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