Structural and Functional Insights into Peptidoglycan Access for the Lytic Amidase LytA of <named-content content-type="genus-species">Streptococcus pneumoniae</named-content>

ABSTRACT The cytosolic N-acetylmuramoyl-l-alanine amidase LytA protein of Streptococcus pneumoniae, which is released by bacterial lysis, associates with the cell wall via its choline-binding motif. During exponential growth, LytA accesses its peptidoglycan substrate to cause lysis only when nascent...

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Autores principales:	Peter Mellroth, Tatyana Sandalova, Alexey Kikhney, Francisco Vilaplana, Dusan Hesek, Mijoon Lee, Shahriar Mobashery, Staffan Normark, Dmitri Svergun, Birgitta Henriques-Normark, Adnane Achour
Formato:	article
Lenguaje:	EN
Publicado:	American Society for Microbiology 2014
Materias:	Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/7bbf23dded394841b27d52760a315892
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spelling	oai:doaj.org-article:7bbf23dded394841b27d52760a3158922021-11-15T15:45:10ZStructural and Functional Insights into Peptidoglycan Access for the Lytic Amidase LytA of <named-content content-type="genus-species">Streptococcus pneumoniae</named-content>10.1128/mBio.01120-132150-7511https://doaj.org/article/7bbf23dded394841b27d52760a3158922014-02-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.01120-13https://doaj.org/toc/2150-7511ABSTRACT The cytosolic N-acetylmuramoyl-l-alanine amidase LytA protein of Streptococcus pneumoniae, which is released by bacterial lysis, associates with the cell wall via its choline-binding motif. During exponential growth, LytA accesses its peptidoglycan substrate to cause lysis only when nascent peptidoglycan synthesis is stalled by nutrient starvation or β-lactam antibiotics. Here we present three-dimensional structures of LytA and establish the requirements for substrate binding and catalytic activity. The solution structure of the full-length LytA dimer reveals a peculiar fold, with the choline-binding domains forming a rigid V-shaped scaffold and the relatively more flexible amidase domains attached in a trans position. The 1.05-Å crystal structure of the amidase domain reveals a prominent Y-shaped binding crevice composed of three contiguous subregions, with a zinc-containing active site localized at the bottom of the branch point. Site-directed mutagenesis was employed to identify catalytic residues and to investigate the relative impact of potential substrate-interacting residues lining the binding crevice for the lytic activity of LytA. In vitro activity assays using defined muropeptide substrates reveal that LytA utilizes a large substrate recognition interface and requires large muropeptide substrates with several connected saccharides that interact with all subregions of the binding crevice for catalysis. We hypothesize that the substrate requirements restrict LytA to the sites on the cell wall where nascent peptidoglycan synthesis occurs. IMPORTANCE Streptococcus pneumoniae is a human respiratory tract pathogen responsible for millions of deaths annually. Its major pneumococcal autolysin, LytA, is required for autolysis and fratricidal lysis and functions as a virulence factor that facilitates the spread of toxins and factors involved in immune evasion. LytA is also activated by penicillin and vancomycin and is responsible for the lysis induced by these antibiotics. The factors that regulate the lytic activity of LytA are unclear, but it was recently demonstrated that control is at the level of substrate recognition and that LytA required access to the nascent peptidoglycan. The present study was undertaken to structurally and functionally investigate LytA and its substrate-interacting interface and to determine the requirements for substrate recognition and catalysis. Our results reveal that the amidase domain comprises a complex substrate-binding crevice and needs to interact with a large-motif epitope of peptidoglycan for catalysis.Peter MellrothTatyana SandalovaAlexey KikhneyFrancisco VilaplanaDusan HesekMijoon LeeShahriar MobasheryStaffan NormarkDmitri SvergunBirgitta Henriques-NormarkAdnane AchourAmerican Society for MicrobiologyarticleMicrobiologyQR1-502ENmBio, Vol 5, Iss 1 (2014)
institution	DOAJ
collection	DOAJ
language	EN
topic	Microbiology QR1-502
spellingShingle	Microbiology QR1-502 Peter Mellroth Tatyana Sandalova Alexey Kikhney Francisco Vilaplana Dusan Hesek Mijoon Lee Shahriar Mobashery Staffan Normark Dmitri Svergun Birgitta Henriques-Normark Adnane Achour Structural and Functional Insights into Peptidoglycan Access for the Lytic Amidase LytA of <named-content content-type="genus-species">Streptococcus pneumoniae</named-content>
description	ABSTRACT The cytosolic N-acetylmuramoyl-l-alanine amidase LytA protein of Streptococcus pneumoniae, which is released by bacterial lysis, associates with the cell wall via its choline-binding motif. During exponential growth, LytA accesses its peptidoglycan substrate to cause lysis only when nascent peptidoglycan synthesis is stalled by nutrient starvation or β-lactam antibiotics. Here we present three-dimensional structures of LytA and establish the requirements for substrate binding and catalytic activity. The solution structure of the full-length LytA dimer reveals a peculiar fold, with the choline-binding domains forming a rigid V-shaped scaffold and the relatively more flexible amidase domains attached in a trans position. The 1.05-Å crystal structure of the amidase domain reveals a prominent Y-shaped binding crevice composed of three contiguous subregions, with a zinc-containing active site localized at the bottom of the branch point. Site-directed mutagenesis was employed to identify catalytic residues and to investigate the relative impact of potential substrate-interacting residues lining the binding crevice for the lytic activity of LytA. In vitro activity assays using defined muropeptide substrates reveal that LytA utilizes a large substrate recognition interface and requires large muropeptide substrates with several connected saccharides that interact with all subregions of the binding crevice for catalysis. We hypothesize that the substrate requirements restrict LytA to the sites on the cell wall where nascent peptidoglycan synthesis occurs. IMPORTANCE Streptococcus pneumoniae is a human respiratory tract pathogen responsible for millions of deaths annually. Its major pneumococcal autolysin, LytA, is required for autolysis and fratricidal lysis and functions as a virulence factor that facilitates the spread of toxins and factors involved in immune evasion. LytA is also activated by penicillin and vancomycin and is responsible for the lysis induced by these antibiotics. The factors that regulate the lytic activity of LytA are unclear, but it was recently demonstrated that control is at the level of substrate recognition and that LytA required access to the nascent peptidoglycan. The present study was undertaken to structurally and functionally investigate LytA and its substrate-interacting interface and to determine the requirements for substrate recognition and catalysis. Our results reveal that the amidase domain comprises a complex substrate-binding crevice and needs to interact with a large-motif epitope of peptidoglycan for catalysis.
format	article
author	Peter Mellroth Tatyana Sandalova Alexey Kikhney Francisco Vilaplana Dusan Hesek Mijoon Lee Shahriar Mobashery Staffan Normark Dmitri Svergun Birgitta Henriques-Normark Adnane Achour
author_facet	Peter Mellroth Tatyana Sandalova Alexey Kikhney Francisco Vilaplana Dusan Hesek Mijoon Lee Shahriar Mobashery Staffan Normark Dmitri Svergun Birgitta Henriques-Normark Adnane Achour
author_sort	Peter Mellroth
title	Structural and Functional Insights into Peptidoglycan Access for the Lytic Amidase LytA of <named-content content-type="genus-species">Streptococcus pneumoniae</named-content>
title_short	Structural and Functional Insights into Peptidoglycan Access for the Lytic Amidase LytA of <named-content content-type="genus-species">Streptococcus pneumoniae</named-content>
title_full	Structural and Functional Insights into Peptidoglycan Access for the Lytic Amidase LytA of <named-content content-type="genus-species">Streptococcus pneumoniae</named-content>
title_fullStr	Structural and Functional Insights into Peptidoglycan Access for the Lytic Amidase LytA of <named-content content-type="genus-species">Streptococcus pneumoniae</named-content>
title_full_unstemmed	Structural and Functional Insights into Peptidoglycan Access for the Lytic Amidase LytA of <named-content content-type="genus-species">Streptococcus pneumoniae</named-content>
title_sort	structural and functional insights into peptidoglycan access for the lytic amidase lyta of <named-content content-type="genus-species">streptococcus pneumoniae</named-content>
publisher	American Society for Microbiology
publishDate	2014
url	https://doaj.org/article/7bbf23dded394841b27d52760a315892
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Structural and Functional Insights into Peptidoglycan Access for the Lytic Amidase LytA of <named-content content-type="genus-species">Streptococcus pneumoniae</named-content>

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