Bacteriophage P1: a new paradigm for control of phage lysis

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Title: Bacteriophage P1: a new paradigm for control of phage lysis
Author: Xu, Min
Abstract: The N -terminal hydrophobic domain of the phage P1 endolysin Lyz was found to facilitate the export of Lyz in a sec -dependent fashion , explaining the ability of Lyz to cause lysis of E .coli in the absence of the P1 holin . The N -terminal domain of Lyz is demonstrated to be both necessary and sufficient not only for export to the membrane but also for release into the periplasm of this endolysin . We propose that this unusual N -terminal domain functions as a "signal arrest - release" (SAR ) sequence , which first directs the endolysin to the periplasm in membrane -tethered form and then allows it to be released as a soluble active enzyme in the periplasm . To understand why release from the membrane is required for the physiological expression of the lytic activity of Lyz , we examined the role of its seven cysteine residues in the biogenesis of the active endolysin . The inactive , membrane -tethered and the active , soluble forms of Lyz differ in their pattern of intramolecular disulfide bonding . We conclude that the release of Lyz from the membrane leads to an intramolecular thiol -disulfide bond isomerization causing a dramatic conformational change in the Lyz protein . As a result , an active site cleft that is missing in nascent Lyz is generated in the mature form of the endolysin . Examination of the protein sequences of related bacteriophage endolysins suggests that the presence of an SAR sequence is not unique to Lyz . Studies on holin and antiholin indicated that P1 encodes two holins , LydA and LydC . The antiholin LydB inhibits LydA by binding to it directly on the membrane . All above results demonstrate a new paradigm for control of phage lysis , which is , upon depolarization of the membrane by holin function at a programmed time , endolysin is released from the bilayer leading to the immediate lysis of the host .
URI: http : / /hdl .handle .net /1969 .1 /2734
Date: 2005-11-01

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Bacteriophage P1: a new paradigm for control of phage lysis. Available electronically from http : / /hdl .handle .net /1969 .1 /2734 .

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