Crystallization and X-ray analysis of the transcription-activator protein C1 of bacteriophage P22 in complex with the PRE promoter element

• Published in: Acta crystallographica. Section F, Structural biology communications Vol. 71; no. 10; pp. 1286 - 1291
• Main Authors: Mondal, Avisek, Chattopadhyaya, Rajagopal, Datta, Ajit Bikram, Parrack, Pradeep
• Format: Journal Article
• Language: English
• Published: 5 Abbey Square, Chester, Cheshire CH1 2HU, England International Union of Crystallography 01.10.2015; Wiley Subscription Services, Inc
• Subjects: Amino Acid Sequence; Bacteriology; Bacteriophage P22 - chemistry; Chromatography, Gel; Crystallization; Crystallography, X-Ray; Deoxyribonucleic acid; DNA; lambda CII; lysis-lysogeny choice; Molecular Sequence Data; P22 C1; phage P22; Promoter Regions, Genetic; Proteins; Research Communications; Sequence Homology, Amino Acid; Viral Proteins - chemistry; P22 C1; lambda CII; phage P22; lysis–lysogeny choice
• ISSN: 2053-230X; 2053-230X
• DOI: 10.1107/S2053230X15015708

The transcription‐activator protein C1 of the temperate phage P22 of Salmonella typhimurium plays a key role in the lytic versus lysogenic switch of the phage. A homotetramer of 92‐residue polypeptides, C1 binds to an approximate direct repeat similar to the transcription activator CII of coliphage λ. Despite this and several other similarities, including 57% sequence identity to coliphage CII, many biochemical observations on P22 C1 cannot be explained based on the structure of CII. To understand the molecular basis of these differences, C1 was overexpressed and purified and subjected to crystallization trials. Although no successful hits were obtained for the apoprotein, crystals could be obtained when the protein was subjected to crystallization trials in complex with a 23‐mer promoter DNA fragment (PRE). These crystals diffracted very well at the home source, allowing the collection of a 2.2 Å resolution data set. The C1–DNA crystals belonged to space group P21, with unit‐cell parameters a = 87.27, b = 93.58, c = 111.16 Å, β = 94.51°. Solvent‐content analysis suggests that the asymmetric unit contains three tetramer–DNA complexes. The three‐dimensional structure is expected to shed light on the mechanism of activation by C1 and the molecular basis of its specificity.