The crystal structure of the major pneumococcal autolysin LytA in complex with a large peptidoglycan fragment reveals the pivotal role of glycans for lytic activity.
The pneumococcal autolysin LytA is a key virulence factor involved in several important functions including DNA competence, immune evasion and biofilm formation. Here, we present the 1.05 Å crystal structure of the catalytic domain of LytA in complex with a synthetic cell-wall-based peptidoglycan (PG) ligand that occupies the entire Y-shaped substrate-binding crevice. As many as twenty-one amino-acid residues are engaged in ligand interactions with a majority of these interactions directed towards the glycan strand. All saccharides are intimately bound through hydrogen bond, van der Waals and CH-π interactions. Importantly, the structure of LytA is not altered upon ligand binding, whereas the bound ligand assumes a different conformation compared to the unbound NMR-based solution structure of the same PG-fragment. Mutational study reveals that several non-catalytic glycan-interacting residues, structurally conserved in other amidases from Gram-positive Firmicutes, are pivotal for enzymatic activity. The three-dimensional structure of the LytA/PG complex provides a novel structural basis for ligand restriction by the pneumococcal autolysin, revealing for the first time an importance of the multivalent binding to PG saccharides.
Science for Life Laboratory, Department of Medicine Solna, Karolinska Institutet, and Department of Infectious Diseases, Karolinska University Hospital, Solna, Stockholm, SE, 17176, Sweden.
Tatyana
T
Sandalova
Departments of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN, 46556, USA.
Mijoon
M
Lee
Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, 171 77, Sweden.|Department of Clinical Microbiology, Karolinska University Hospital, Solna, Stockholm, 17176, Sweden.
Birgitta
B
Henriques-Normark
Departments of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN, 46556, USA.
Dusan
D
Hesek
Departments of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN, 46556, USA.
Shahriar
S
Mobashery
Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, 171 77, Sweden. peter.mellroth@ki.se.|Department of Clinical Microbiology, Karolinska University Hospital, Solna, Stockholm, 17176, Sweden. peter.mellroth@ki.se.
Peter
P
Mellroth
Science for Life Laboratory, Department of Medicine Solna, Karolinska Institutet, and Department of Infectious Diseases, Karolinska University Hospital, Solna, Stockholm, SE, 17176, Sweden. adnane.achour@ki.se.
Adnane
A
Achour
D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D020134:Catalytic Domain; D002473:Cell Wall / Q000201:enzymology / Q000378:metabolism; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000737:chemistry* / Q000378:metabolism*; D010457:Peptidoglycan / Q000737:chemistry* / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D013296:Streptococcus pneumoniae / Q000201:enzymology / Q000378:metabolism; D013329:Structure-Activity Relationship
D001426:Bacterial Proteins; D010457:Peptidoglycan; D021122:Protein Subunits; D009238:N-Acetylmuramoyl-L-alanine Amidase