Further studies on low molecular weight crystalline: Relationship between the bovine βSthe human 24kD protein and the γ-crystallins

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Abstract
Three classes of monomeric crystalline separable by SDS gel electrophoresis or by gel filtration have been demonstrated in human lens. In previous studies we have concluded from physico-chemical and immunological data that all three polypeptides are related and should be classified as γ-crystallins. The present paper presents further evidence supporting this conclusion, but also demonstrates that the 24,000 dalton (24kD) polypeptide corresponds to the βS-crystallin. βS-crystallin was purified by classical techniques from bovine lens and was shown to cross-react with a monoclonal antibody specific for the human 24kD polypeptide. This antibody exhibited no reactivity to other crystallin fractions from either bovine or human lenses. The identification of the 24kD polypeptide as βS was further supported by analysis of the tertiary structures of the molecules by near UV-circular dichroism and by the finding of a blocked amino terminus on the 24kD polypeptide. Our finding that the human βS (24kD polypeptide) should actually be classified as a γ-crystallin is fully consistent with recently reported sequence data on bovine βS-crystallin.