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A holin/peptidoglycan hydrolase-dependent protein secretion system

Lookup NU author(s): Professor Tracy Palmer FRS FRSE FMedSciORCiD, Dr Alexander FinneyORCiD, Gary Atkinson, Professor Frank SargentORCiD



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Gram-negative bacteria have evolved numerous pathways to secrete proteins across their complex cell envelopes. Here, we describe a protein secretion system which uses a holin membrane protein in tandem with a cell wall editing enzyme to mediate the secretion of substrate proteins from the periplasm to the cell exterior. The identity of the cell wall editing enzymes employed was found to vary across biological systems. For instance, the chitinase secretion pathway of Serratia marcescens uses an endopeptidase to facilitate secretion, whereas the secretion of Typhoid toxin in Salmonella enterica serovar Typhi relies on a muramidase. Various families of holins are also predicted to be involved. Genomic analysis indicates that this pathway is conserved and implicated in the secretion of hydrolytic enzymes and toxins for a range of bacteria. The pairing of holins from different families with various types of peptidoglycan hydrolases suggests that this secretion pathway evolved multiple times. We suggest that the complementary bodies of evidence presented is sufficient to propose that the pathway be named the Type 10 Secretion System (TXSS). Potential mechanisms for secretion across the outer membrane are discussed.

Publication metadata

Author(s): Palmer T, Finney A, Saha CK, Atkinson GC, Sargent F

Publication type: Review

Publication status: Published

Journal: Molecular Microbiology

Year: 2021

Volume: 115

Issue: 3

Pages: 345-355

Print publication date: 01/03/2021

Online publication date: 04/09/2020

Acceptance date: 26/08/2020

ISSN (print): 0950-382X

ISSN (electronic): 1365-2958


DOI: 10.1111/mmi.14599