Figure 1
From: Mouse Antibody of IgM Class is Prone to Non-Enzymatic Cleavage between CH1 and CH2 Domains
Mouse μ’ chain is generated by specific cleavage after Asn209 in IgM heavy chain constant region. (a) Estimation of μ’ chain molecular mass. Three different IgMs were deglycosylated using PNGase F. Glycosylated μ‘ chain is a 55 kDa protein. It consists of a ∼40 kDa polypeptide and five N-glycans, which total Mw is about 15 kDa. The gel was stained using silver nitrate. deglyc. – deglycosylated; HC – heavy chain; LC – light chain. (b) MS analysis of μ’ chains derived from O10 and Q6 IgMs. The charts present sequence coverage and numbers of detected peptides obtained from μ’ chain by trypsin- or V8 digestion. (c) N-terminal sequences of μ’ chains derived from three different IgMs determined by Edman degradation. Grey letters indicate uncertain residues. (d) Domains of full-length IgM heavy chain. Arrowheads indicate N-glycosylation sites. The site of cleavage resulting in μ’ chain is shown with an arrow. (e) Model of CH1 and CH2 domains of mouse IgM. Asn209 is in a solvent accessible loop. The model was generated using I-TASSER server47,48 and visualized in PyMOL (Schrödinger). (f) Asn209 precedes the CH1-CH2 linker. (g) Asn209 is surrounded by charged amino acids. (h) IgM heavy chain cleavage occurs within CH1 domain after Asn209 (marked in bold). There is a polymorphism in amino acid residue 209 between mouse strains C57 (Lys209) and Balb/c (Arg209).
