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The lytic cassette of mycobacteriophage Ms6 encodes an enzyme with lipolytic activity

¹ Unidade dos Retrovirus e Infecções Associadas, Centro de Patogénese Molecular, Faculty of Pharmacy, University of Lisbon, Portugal
² Unidade de Biologia Molecular e Biopatologia Experimental, iMed, Faculty of Pharmacy, University of Lisbon, Portugal
³ Department of Microbiology Immunology and Pathology, Colorado State University, Fort Collins, CO 80523, USA

Correspondence
Madalena Pimentel
mpimentel{at}ff.ul.pt

dsDNA bacteriophages use the dual system endolysin–holin to achieve lysis of their bacterial host. In addition to these two essential genes, some bacteriophages encode additional proteins within their lysis module. In this report, we describe the activity of a protein encoded by gene lysB from the mycobacteriophage Ms6. lysB is localized within the lysis cassette, between the endolysin gene (lysA) and the holin gene (hol). Analysis of the deduced amino acid sequence of LysB revealed the presence of a conserved motif (Gly-Tyr-Ser-Gln-Gly) characteristic of enzymes with lipolytic activity. A BLAST search within the sequences of protein databases revealed significant similarities to other putative proteins that are encoded by mycobacteriophages only, indicating that LysB and those proteins may be specific to their mycobacterial hosts. A screening for His₆-LysB activity on esterase and lipase substrates confirmed the lipolytic activity. Examination of the kinetic parameters of recombinant His₆-LysB for the hydrolysis of p-nitrophenyl esters indicated that although this protein could use a wide range of chain length substrates (C₄–C₁₈), it presents a higher affinity for p-nitrophenyl esters of longer chain length (C₁₆ and C₁₈). Using p-nitrophenyl butyrate as a substrate, the enzyme showed optimal activity at 23 °C and pH 7.5–8.0. Activity was increased in the presence of Ca²⁺ and Mn²⁺. To the best of our knowledge, this is the first description of a protein with lipolytic activity encoded within a bacteriophage.