Table of Contents
ISRN Immunology
Volume 2013, Article ID 676703, 6 pages
http://dx.doi.org/10.1155/2013/676703
Research Article

Partial Characterization of Immunoglobulin C Gene of Water Buffalo (Bubalus bubalis) Predicts Distinct Structural Features of C1q-Binding Site in C 3 Domain

1Department of Molecular and Cellular Biology, SCIE4248, University of Guelph, 50 Stone Road E, Guelph, ON, Canada N1G 2W1
2National Specialist Meat Processing and Microbiology, Meat Programs Division, Canadian Food Inspection Agency, 1400 Merivale Road, Ottawa, ON, Canada K1A 0Y9
3Department of Veterinary Microbiology, Punjab Agricultural University, Ludhiana 141 004, India
4Microbiology Section, Division of Fish Health Management, Central Institute of Freshwater Aquaculture, Bhubaneswar, Orissa 751 002, India

Received 6 May 2013; Accepted 7 June 2013

Academic Editors: J. L. Stafford and F. M. Ubeira

Copyright © 2013 Surinder S. Saini et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Partial characterization of immunoglobulin C gene of water buffalo (Bubalus bubalis) revealed high amino acid sequence identity with C of cattle (94.28%) and sheep (91.71%). Four amino acid replacements (Met-301, Val-310, Asn-331, and Thr-432) in C 2, C 3, and C 4 of buffalo IgM are distinct, however. Unlike cattle, a codon deletion (GTG encoding valine at position 507 in cattle) and an insertion (GGC encoding glycine at position 532) occur in buffalo C 4. Three N-linked glycosylation (Asn-X-Thr/Ser) sites (one at position 325–327 in C 2; two at positions 372–374 and 394–396 in C 3) differentiate buffalo IgM from cattle and sheep. Similar to cattle, buffalo IgM has fewer prolines in C 2, which acts as hinge, which restricts Fab arm flexibility. Increased structural flexibility of the C1q-binding site in C 3 compensates for the rigid buffalo C 2 domain. Secondary structure of C1q-binding site is distinct in buffalo and cattle IgM where long alpha-helical structure is predominant that may be relevant to complement fixation function. Conserved protein motif “Thr-Cys-Thr-Val-Ala-His” provides protein signatures of C1q-binding region of ruminant species. The distinct structural features of C1q-binding site of buffalo and cattle IgM seem to be of functional significance and, therefore, useful in designing antibody based therapeutics.