Partial amino acid sequence of the V region of A κ-type Bence Jones cryoprotein

The amino acid sequence of the human Bence Jones cryoprotein Ver is reported. This protein is remarkable for its ability to crystallize at 4°C and for its unusual amino acid composition.

For structure determination, the protein was fully reduced and car☐ymethylated, then digested with trypsin or chymotrypsin. Eighteen tryptic peptides and 27 chymotryptic peptides were isolated by column and paper chromatography. Complete or partial sequences were obtained for all peptides covering the variable half of the chain, using traditional sequencing methods. Peptides of the constant region were submitted only to amino acid analysis.

The cryoprotein Ver seems to have many similarities with the Bence Jones proteins of the V_kIII type. although unusual substitutions occur in many places along the chain. The protein lacks a certain number of basic amino acids in the variable region and shows an increased number of hydrophobic residues. For that reason, some of the peptides of the variable region are large and poorly soluble.