Posttranslational modifications in human plasma MBL and human recombinant MBL.
Mannan-binding lectin (MBL) is a complex serum protein that plays an important role in innate immunity. In addition to assuming several different oligomeric forms, the polypeptide itself is highly heterogeneous. This heterogeneity is due to post-translational modifications, which help to stabilize the intact protein in its active conformation. For the first time, positions and occupation frequency of partial hydroxylations and partial glycosylations are reported in MBL. Hydroxylation and glycosylation patterns of both recombinant and plasma derived MBL were determined, using a combination of mass spectrometry on reduced MBL and on enzyme cleaved MBL. Variations in the degree of hydroxylation and glycosylation seem to be an indigenous characteristic of collectins. In addition to these already known modifications, a new post-translational modification was identified. Cys(216) (and occasionally also Cys(202)) was modified in trace amounts to dehydroalanine, as detected by a 34 Da mass loss. This impairs the formation of a disulphide bond in the carbohydrate recognition domain. The dehydroalanine was identified in similar small amounts in both recombinant and plasma-derived MBL.
Jensen
Pia Hønnerup
PH
Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark.
Laursen
Inga
I
Matthiesen
Finn
F
Højrup
Peter
P
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D006031:Glycosylation; D006801:Humans; D006900:Hydroxylation; D037601:Mannose-Binding Lectin / Q000097:blood* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000097:blood / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D000596:Amino Acids; D037601:Mannose-Binding Lectin; D010455:Peptides; D011994:Recombinant Proteins