Alteration in the ubiquitin structure and function in the human lens: a possible mechanism of senile cataractogenesis

High-performance liquid chromatography purification followed by
mass spectrometry analyses highlighted that human senile
cataractous lens includes a 8182 Da species which is absent in the
normal lens, whereas a 8566/8583 Da species is present in both
lenses. Western blot analysis identified both species as ubiquitin.
The species at lower molecular weight is a shorter form due to the
cleavage of the C-terminal residues 73-76. As it is the last amino
acid of ubiquitin which is involved in the protein degradation
mechanism, we suggest that this structure modification
compromises the function of ubiquitin and consequently the
physiologically occurring degradation of the lens proteins.