P22 bacteriophage has been studied extensively and has served as a model for many important processes such as in vivo protein folding, protein aggregation and protein-protein interactions. The trimeric tailspike protein (TSP) serves as the receptor-binding protein for the P22 bacteriophage to the bacterial host. The homotrimeric P22 tail consists of three chains of 666aa in which the first 108aa form a trimeric dome-like structure which is called the N-terminal domain (NTD) and is responsible for attachment of the tailspike protein to the rest of the phage particle structure in the phage assembly pathway. Knowledge of this interaction requires information on what amino acids are interacting in the interface and how the NTD structure is maintained. The first 23aa form the "stem peptide" which originates at the dome top and terminates at the dome bottom. It contains a hydrophobic valine patch (V8-V9-V10) located within the dome structure. It is hypothesized that the interaction between the hydrophobic valine patch located on stem peptide and the adjacent polypeptide is critical for the interchain interaction which should be important for the stability of the P22 TSP NTD itself. To test this hypothesis, each amino acid in the valine residues is substituted by an acid, a basic, and a hydrophobic amino acid. The results of such substitutions are presented as well as associated studies. The data strongly suggest that the valine patch is of critical importance in the hydrophobic interaction between stem peptide valine patch and an adjacent chain.
The P22 tailspike protein is an intensely studied protein whose structure and sequence has been described. However, a study, describing important protein interactions related to its function at the N-terminal domain, has been lacking. The P22 tailspike protein (TSP) consists of three identical polypeptide chains of 666aa. The first 108 of the 666aa in the P22 TSP form a trimeric N-terminal domain (NTD). Each of the three chains of the trimeric NTD contributes to the formation of a dome-like structure. Our studies suggest that a short stretch of amino acids located within the first fifteen amino acids of the P22 TSP NTD is critical for the stability of the dome structure formed by the first 108aa of the P22 TSP NTD. The first 23aa are located within this dome-like structure and have been dubbed the "stem" of the NTD. Although amino acid residues in the first 15aa (lower stem) are critical, deletion analysis and in vitro assembly studies implicate the rest of the stem in additional stabilizing interactions. Our studies implicate a common protein-protein interaction motif made up of interchain hydrophobic contacts between adjacent chains
The P22 phage system is an intensely studied model system. Studies have ranged from biochemical analysis of basic life processes to the use of this phage for phage therapy. The phage tailspike protein (TSP) has itself been the subject of intensive studies over the past fifty years. The P22 TSP is essential for initiation of the infection process and instrumental as the last protein assembled onto the phage particle structure to complete its assembly. It has also been the subject for many structural studies including cryoelectron microscopic analysis and photophysical studies. It has been a model for in vivo and in vitro protein folding including analysis using P22 TSP temperaturesensitive for folding mutations (tsf). Recently the structure and function of the N-terminal domain (NTD), including some aspects of the structural stability of the P22 TSP NTD (aa1-aa108), are being genetically dissected. This report strongly supports the notion that two amino acids, not localized to the internal NTD dome stem, are important in the structural stability of the P22 TSP NTD.
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