βγ-CAT is a naturally existing protein complex of non-lens bg-crystallin and trefoil factor, purified from
Bombina maxima
skin secretions. In HUVECs, βγ-CAT can be rapidly endocytosed via intracellular vacuole formation and translocated to the nucleus to regulate cell fuction. In this paper, we found that it contains conserved Walker B motifs (IILYDEPS, residues 6-13) and Walker A motifs (GQSLSGKS, residues 96-103) in the βγ-CAT a-subunit sequence. βγ-CAT showed potential NTP-binding and weak GTPase/ATPase activities
in vitro. Through Western blotting analysis, we found that the a- and b-subunits of βγ-CAT participated in a 150 kDa SDS-stable protein complex formation, which also contained positive ubiquitination signals in the βγ-CAT treated HUVEC. Furthermore，under confocal microscopy, the immunofluorescence signals of ubiquitin and βγ-CAT subunits were co-localized in the vacuoles that were distributed in the cytoplasm and nucleus. In addition, βγ-CAT could induce several tumor cell’s detachment and apoptosis, and selectively kill tumor cells. These findings provide a clue to understand the mechanism of βγ-CAT endocysis and nuclear transport, and give an insight to investigate the possible occurrence of similar molecule’s cellular functions and action mechanisms of non-lens bg-crystallins and trefoil factors in mammals.
