Structure and function of phage p2 ORF34p2, a new type of single‐stranded DNA binding protein

Abstract

Lactococcus lactis, a Gram-positive bacterium widely used by the dairy industry, is subject to infection by a diverse population of virulent phages, predominantly by those of the 936 group, including the siphovirus phage p2. Confronted with the negative impact of phage infection on milk fermentation, the study of the biology of lactococcal provides insight from applied and fundamental perspectives. We decided to characterize the product of the orf34 gene from lactococcus phage p2, which was considered as a candidate single-stranded DNA binding protein (SSB) due to its localization downstream of a gene coding for a single-strand annealing protein. Two-dimensional gel electrophoresis showed that ORF34p2 is expressed in large amounts during the early phases of phage infection, suggesting an important role in this process. Gel-shift assays, surface plasmon resonance and atomic force microscopy demonstrated that ORF34p2 interacts with single-strand DNA with nanomolar affinity. We also determined the crystal structure of ORF34p2 and showed that it bears a variation of the typical oligonucleotide/oligosaccharide binding-fold of SSBs. Finally, we found that ORF34p2 is able to stimulate Escherichia coli RecA-mediated homologous recombination. The specific structural and biochemical properties that distinguish ORF34p2 from other SSB proteins are discussed.