TY - JOUR

T1 - The Phage T4 Antiholin RI Has a Cleavable Signal Peptide, Not a SAR Domain

AU - Mehner-Breitfeld, Denise

AU - Schwarzkopf, Jan Michel Frederik

AU - Young, Ry

AU - Kondabagil, Kiran

AU - Brüser, Thomas

N1 - Funding Information: This work was funded by the German federal state Lower Saxony. The publication of this article was funded by the Open Access Fund of the Leibniz Universität Hannover.

PY - 2021/8/11

Y1 - 2021/8/11

N2 - Holin/endolysin-mediated lysis of phage T4 of Escherichia coli is tightly regulated by the antiholins RI and RIII. While regulation by the cytoplasmic RIII plays a minor role, the periplasmic antiholin RI binds tightly to the holin T and is believed to directly sense periplasmic phage DNA from superinfections as a trigger for the inhibition of lysis. RI has been reported to contain a non-cleavable signal peptide that anchors the protein to the membrane. Lysis is believed to be induced at some stage by a membrane depolarization that causes a release of RI into the periplasm without cleavage of the signal anchor. For the current model of phage lysis induction, it is thus a fundamental assumption that the N-terminal trans-membrane domain (TMD) of RI is such a signal anchor release (SAR) domain. Here we show that, in contrast to previous reports, this domain of RI is a cleavable signal peptide. RI is processed and released into the periplasm as a mature protein, and inactivation of its signal peptidase cleavage site blocks processing and membrane release. The signal peptide of RI can also mediate the normal translocation of a well-characterized Sec substrate, PhoA, into the periplasm. This simplifies the current view of phage lysis regulation and suggests a fundamentally different interpretation of the recently published structure of the soluble domains of the RI–T complex.

AB - Holin/endolysin-mediated lysis of phage T4 of Escherichia coli is tightly regulated by the antiholins RI and RIII. While regulation by the cytoplasmic RIII plays a minor role, the periplasmic antiholin RI binds tightly to the holin T and is believed to directly sense periplasmic phage DNA from superinfections as a trigger for the inhibition of lysis. RI has been reported to contain a non-cleavable signal peptide that anchors the protein to the membrane. Lysis is believed to be induced at some stage by a membrane depolarization that causes a release of RI into the periplasm without cleavage of the signal anchor. For the current model of phage lysis induction, it is thus a fundamental assumption that the N-terminal trans-membrane domain (TMD) of RI is such a signal anchor release (SAR) domain. Here we show that, in contrast to previous reports, this domain of RI is a cleavable signal peptide. RI is processed and released into the periplasm as a mature protein, and inactivation of its signal peptidase cleavage site blocks processing and membrane release. The signal peptide of RI can also mediate the normal translocation of a well-characterized Sec substrate, PhoA, into the periplasm. This simplifies the current view of phage lysis regulation and suggests a fundamentally different interpretation of the recently published structure of the soluble domains of the RI–T complex.

KW - antiholins

KW - holins

KW - lysis inhibition

KW - phage lysis

KW - SAR domain

KW - signal peptide

UR - http://www.scopus.com/inward/record.url?scp=85113448319&partnerID=8YFLogxK

U2 - 10.3389/fmicb.2021.712460

DO - 10.3389/fmicb.2021.712460

M3 - Article

VL - 12

JO - Frontiers in Microbiology

JF - Frontiers in Microbiology

SN - 1664-302X

M1 - 712460

ER -