TY - JOUR

T1 - Occurrence and potential mechanism of holin-mediated non-lytic protein translocation in bacteria

AU - Brüser, Thomas

AU - Mehner-Breitfeld, Denise

N1 - Funding Information: We thank Ralf Gerhard (Medical High School Hannover, Germany) and Jörg Overmann (DSMZ Braunschweig, Germany) for helpful discussions. We thank Anders Krogh (University of Copenhagen, Denmark) for discussion of TMHMM predictions. This study was supported by the state of Lower Saxony.

PY - 2022/9/23

Y1 - 2022/9/23

N2 - Holins are generally believed to generate large membrane lesions that permit the passage of endolysins across the cytoplasmic membrane of prokaryotes, ultimately resulting in cell wall degradation and cell lysis. However, there are more and more examples known for non-lytic holin-dependent secretion of proteins by bacteria, indicating that holins somehow can transport proteins without causing large membrane lesions. Phage-derived holins can be used for a non-lytic endolysin translocation to permeabilize the cell wall for the passage of secreted proteins. In addition, clostridia, which do not possess the Tat pathway for transport of folded proteins, most likely employ non-lytic holin-mediated transport also for secretion of toxins and bacteriocins that are incompatible with the general Sec pathway. The mechanism for non-lytic holin-mediated transport is unknown, but the recent finding that the small holin TpeE mediates a non-lytic toxin secretion in Clostridium perfringens opened new perspectives. TpeE contains only one short transmembrane helix that is followed by an amphipathic helix, which is reminiscent of TatA, the membrane-permeabilizing component of the Tat translocon for folded proteins. Here we review the known cases of non-lytic holin-mediated transport and then focus on the structural and functional comparison of TatA and TpeE, resulting in a mechanistic model for holin-mediated transport. This model is strongly supported by a so far not recognized naturally occurring holin-endolysin fusion protein.

AB - Holins are generally believed to generate large membrane lesions that permit the passage of endolysins across the cytoplasmic membrane of prokaryotes, ultimately resulting in cell wall degradation and cell lysis. However, there are more and more examples known for non-lytic holin-dependent secretion of proteins by bacteria, indicating that holins somehow can transport proteins without causing large membrane lesions. Phage-derived holins can be used for a non-lytic endolysin translocation to permeabilize the cell wall for the passage of secreted proteins. In addition, clostridia, which do not possess the Tat pathway for transport of folded proteins, most likely employ non-lytic holin-mediated transport also for secretion of toxins and bacteriocins that are incompatible with the general Sec pathway. The mechanism for non-lytic holin-mediated transport is unknown, but the recent finding that the small holin TpeE mediates a non-lytic toxin secretion in Clostridium perfringens opened new perspectives. TpeE contains only one short transmembrane helix that is followed by an amphipathic helix, which is reminiscent of TatA, the membrane-permeabilizing component of the Tat translocon for folded proteins. Here we review the known cases of non-lytic holin-mediated transport and then focus on the structural and functional comparison of TatA and TpeE, resulting in a mechanistic model for holin-mediated transport. This model is strongly supported by a so far not recognized naturally occurring holin-endolysin fusion protein.

KW - Holine

KW - Proteintransport

KW - holins

KW - protein translocation

KW - clostridia

KW - toxins

KW - bacteriocins

KW - endolysins

KW - Tat transport

UR - http://www.scopus.com/inward/record.url?scp=85140920595&partnerID=8YFLogxK

U2 - 10.15698/mic2022.10.785

DO - 10.15698/mic2022.10.785

M3 - Article

VL - 9

SP - 159

EP - 173

JO - Microbial Cell

JF - Microbial Cell

IS - 10

ER -