Previous Article | Next Article ![]()
J. Bacteriol., May 1996, 2498-2506, Vol 178, No. 9
KM Dobos, KH Khoo, KM Swiderek, PJ Brennan and JT Belisle
Chemical evidence for the true glycosylation of mycobacterial proteins was
recently provided in the context of the 45-kDa MPT 32 secreted protein of
Mycobacterium tuberculosis (K. Dobos, K. Swiderek, K.-H. Khoo, P. J.
Brennan, and J. T. Belisle, Infect. Immun. 63:2846-2853, 1995). However,
the full extent and nature of glycosylation as well as the location of
glycosylated amino acids remained undefined. First, to examine the nature
of the covalently attached sugars, the 45-kDa protein was obtained from
cells metabolically labeled with D-[U-14C] glucose and subjected to
compositional analysis, which revealed mannose as the only covalently bound
sugar. Digestion of the protein with the endoproteinase subtilisin and
analysis of products by liquid chromatography-electrospray-mass
spectrometry on the basis of fragments demonstrating neutral losses of
hexose (m/z 162) or pentose (m/z 132) revealed five glycopeptides, S7, S18,
S22, S29, and S41 among a total of 50 peptides, all of which produced only
m/z 162 fragmentation ion deletions. Fast atom bombardment-mass
spectrometry, N-terminal amino acid sequencing, and alpha-mannosidase
digestion demonstrated universal O glycosylation of Thr residues with a
single alpha-D-Man, mannobiose, or mannotriose unit. Linkages within the
mannobiose and mannotriose were all alpha 1-2, as proven by gas
chromatography-mass spectrometry of oligosaccharides released by
beta-elimination. Total sequences of many of the glycosylated and
nonglycosylated peptides combined with published information on the deduced
amino acid sequence of the entire 45-kDa protein demonstrated that the
sites of glycosylation were located in Pro-rich domains near the N terminus
and C terminus of the polypeptide backbone. Specifically, the Thr residues
at positions 10 and 18 were substituted with
alpha-D-Manp(1-->2)alpha-D-Manp, the Thr residue at position 27 was
substituted with a single alpha-D-Manp, and Thr-277 was substituted with
either alpha-D-Manp, alpha-D-Manp(1-- >2)alpha-D-Manp, or
alpha-D-Manp(1--> 2)alpha-D-Manp(1-->2)alpha-D- Manp. This report
further corroborates the existence of true prokaryotic glycoproteins,
defines the complete structure of a mycobacterial mannoprotein and the
first complete structure of a mannosylated mycobacterial protein, and
establishes the principles for the study of other mycobacterial
glycoproteins.
Copyright © 1996, American Society for Microbiology
Definition of the full extent of glycosylation of the 45-kilodalton glycoprotein of Mycobacterium tuberculosis
Department of Microbiology, Colorado State University, Fort Collins 80523, USA.
This article has been cited by other articles:
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»