NATURAL CATALYTIC ANTIBODIES - PEPTIDE-HYDROLYZING ACTIVITIES OF BENCE-JONES PROTEINS AND V-L FRAGMENT

Monoclonal human light chains, i.e. Pence Jones proteins, and their recombinant variable fragments (V-L) were screened for proteolytic activity using peptide-methylcoumarinamide (peptide-MCA) conjugates and vasoactive intestinal polypeptide (VIP) as substrates. Sixteen of 21 Pence Jones proteins and one of three V-L fragments were capable of detectable cleavage of one or more substrates. The magnitude and kinetic characteristics of the activity varied with different substrates. Among the peptide-MCA substrates, the presence of tripeptide or tetrapeptide moieties with a basic residue at the scissile bond generally favored expression of the activity. The influence of N-terminal flanking residue recognition was evident from differing values of K-m and k(cat) (turnover number) observed using different Arg-containing peptide-MCA substrates. Different light chains displayed different kinetic parameters for the same substrate, suggesting unique catalytic sites. Hydrolysis of VIP was characterized by nanomolar Michaelis-Menten constants (K-m), suggesting comparatively high affinity recognition of this peptide, The 25-kDa monomer and the 50-kDa dimer forms of one light chain preparation were resolved by gel filtration in 6 M guanidine hydrochloride, Following renaturation, the monomer displayed 51-fold greater peptide-MCA-hydrolyzing activity than the dimer. A renatured V-L domain prepared by gel filtration in 6 M guanidine hydrochloride displayed VIP-hydrolyzing activity in the 12.5-kDa peak fractions. These results provide evidence for the proteolytic activity of certain human light chains and imply that this phenomenon may have a pathophysiological significance.