Thermodynamic Compatibility of Substrate Proteins Affects Their Cross-Linking by Transglutaminase

Abstract

The formation of heterologous dimers and polymers between different proteins by transglutaminase reaction was studied. Although β-casein and β-lactoglobulin formed homologous polymers in single-substrate systems, only β-casein was polymerized; β-lactoglobulin became a nonreactive substrate in a β-casein/β-lactoglobulin binary system. In contrast, succinylated β-casein formed heterologous dimers, trimers, and oligomers with β-lactoglobulin. Also, β-casein did not form a heterologous dimer or polymer with bovine serum albumin (BSA), whereas α-lactalbumin formed a heterologous dimer and polymer with BSA. Analyses of reaction products of other binary systems, such as α-lactalbumin/β-casein, β-lactoglobulin/ovalbumin, and α-lactalbumin/ovalbumin, suggested that heterologous cross-linking between two proteins by transglutaminase probably depends on the thermodynamic compatibility of mixing of the substrate proteins at the enzyme's active site. Thus, cross-linking between dissimilar proteins, such as caseins and albumins, is not possible, whereas cross-linking between similar proteins, e.g., albumins, globulins, and caseins, can occur. Keywords: Transglutaminase; protein cross-linking; thermodynamic compatibility