Multiple functional roles of the accessory I-domain of bacteriophage P22 coat protein revealed by NMR structure and CryoEM modeling.
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 β-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 β-barrel that anchors the I-domain to a negatively charged surface of the coat protein HK97-core.
Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269, USA.
Alessandro A
AA
Rizzo
Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269, USA.
Margaret M
MM
Suhanovsky
Verna and Marrs McLean Department of Biochemistry and Molecular Biology, National Center for Macromolecular Imaging, Baylor College of Medicine, Houston, TX 77030, USA.
Matthew L
ML
Baker
Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269, USA.
LaTasha C R
LC
Fraser
Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA.
Lisa M
LM
Jones
Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA.
Don L
DL
Rempel
Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA.
Michael L
ML
Gross
Verna and Marrs McLean Department of Biochemistry and Molecular Biology, National Center for Macromolecular Imaging, Baylor College of Medicine, Houston, TX 77030, USA.
Wah
W
Chiu
Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269, USA. Electronic address: andrei.alexandrescu@uconn.edu.
Andrei T
AT
Alexandrescu
Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269, USA; Department of Chemistry, University of Connecticut, Storrs, CT 06269, USA. Electronic address: teschke@uconn.edu.
Carolyn M
CM
Teschke
D017100:Bacteriophage P22 / Q000737:chemistry* / Q000648:ultrastructure*; D036022:Capsid Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D020285:Cryoelectron Microscopy; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D019906:Nuclear Magnetic Resonance, Biomolecular; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D055672:Static Electricity
D036022:Capsid Proteins; D021122:Protein Subunits