Biochemical characterization of a Neisseria meningitidis polysialyltransferase reveals novel functional motifs in bacterial sialyltransferases.
The extracellular polysaccharide capsule is an essential virulence factor of Neisseria meningitidis, a leading cause of severe bacterial meningitis and sepsis. Serogroup B strains, the primary disease causing isolates in Europe and America, are encapsulated in alpha-2,8 polysialic acid (polySia). The capsular polymer is synthesized from activated sialic acid by action of a membrane-associated polysialyltransferase (NmB-polyST). Here we present a comprehensive characterization of NmB-polyST. Different from earlier studies, we show that membrane association is not essential for enzyme functionality. Recombinant NmB-polyST was expressed, purified and shown to synthesize long polySia chains in a non-processive manner in vitro. Subsequent structure-function analyses of NmB-polyST based on refined sequence alignments allowed the identification of two functional motifs in bacterial sialyltransferases. Both (D/E-D/E-G and HP motif) are highly conserved among different sialyltransferase families with otherwise little or no sequence identity. Their functional importance for enzyme catalysis and CMP-Neu5Ac binding was demonstrated by mutational analysis of NmB-polyST and is emphasized by structural data available for the Pasteurella multocida sialyltransferase PmST1. Together our data are the first description of conserved functional elements in the highly diverse families of bacterial (poly)sialyltransferases and thus provide an advanced basis for understanding structure-function relations and for phylogenetic sorting of these important enzymes.
Abteilung Zelluläre Chemie, Medizinische Hochschule Hannover, Carl-Neuberg-Str. 1, 30625 Hannover, Germany.
Friedrich
F
Freiberger
Heike
H
Claus
Almut
A
Günzel
Imke
I
Oltmann-Norden
Justine
J
Vionnet
Martina
M
Mühlenhoff
Ulrich
U
Vogel
Willie F
WF
Vann
Rita
R
Gerardy-Schahn
Katharina
K
Stummeyer
D000293:Adolescent; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002648:Child; D006801:Humans; D008589:Meningococcal Infections / Q000201:enzymology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D038541:Neisseria meningitidis, Serogroup B / Q000201:enzymology*; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D012794:Sialic Acids / Q000378:metabolism; D012799:Sialyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D011993:Recombinant Fusion Proteins; D012794:Sialic Acids; C021319:polysialic acid; D012799:Sialyltransferases