ABSTRACT
CRBP(II) has an uncommon structural heterogeneity. When isolated from either rat pups or adult rat intestine, it resolves into two equally abundant forms
Complete structure determination revealed that the two forms differ only in their N-terminal processing: one form is acetylated at its N terminus whereas the other is not. Acetylation is generally a cotranslational event and is sequencedriven. In vitro studies have determined the effect of N-terminal sequence on acetylation and include an engineered example that duplicates the initial sequence of CRBP(II) and leads to 50% acetylation as observed in vivo for CRBP(II) (50). Two forms of CRBP(II) are also obtained from humans, presumably also differing inN-terminal acetylation The difference in acetylation does not produce any measurable difference in binding properties. While no physiological significance can yet be attached to the presence of two such closely related forms, the unacetylated form was originally isolated with a considerably greater amount of endogenous retinol bound, suggesting the possibility of differential interactions of the two forms within the cell (36).
