Alteration of a developmentally regulated, heat-stable polypeptide in the lens of the Philly mouse. Implications for cataract formation

The β-crystallin basic principal polypeptide (βBp) appears to be altered in the lens of the Philly mouse and may be the main defect in this hereditary cataract. Northern blot analysis showed that an mRNA encoding for βBp is present in the Philly mouse lens, but normal βBp could not be detected. Instead, a different protein related to βBp has been observed. Western blot analysis with antibodies against specific βBp peptide sequences showed that the Philly protein shares the same amino-terminal residue as βBp but lacks a part of the carboxyl-terminal half of normal βBp. The altered protein is slightly smaller than βBp and has a more acidic isoelectric point by two-dimensional gel electrophoresis. It also lacks the property of heat stability characteristic of normal βBp. The mapping of the alteration in βBp may give insight into the nature of the heat stability of this protein as well as some indication of the structural components that are necessary to maintain optical clarity in the lens.