SecA, a remarkable nanomachine

Biological cells harbor a variety of molecular machines that carry out mechanical work at the nanoscale. One of these nanomachines is the bacterial motor protein SecA which translocates secretory proteins through the protein-conducting membrane channel SecYEG. SecA converts chemically stored energy in the form of ATP into a mechanical force to drive polypeptide transport through SecYEG and across the cytoplasmic membrane. In order to accommodate a translocating polypeptide chain and to release transmembrane segments of membrane proteins into the lipid bilayer, SecYEG needs to open its central channel and the lateral gate. Recent crystal structures provide a detailed insight into the rearrangements required for channel opening. Here, we review our current understanding of the mode of operation of the SecA motor protein in concert with the dynamic SecYEG channel. We conclude with a new model for SecA-mediated protein translocation that unifies previous conflicting data

Increased globotriaosylceramide levels in a transgenic mouse expressing human α1,4-galactosyltransferase and a mouse model for treating Fabry disease

Fabry disease is a lysosomal storage disorder caused by an α-galactosidase A (α-Gal A) deficiency and resulting in the accumulation of glycosphingolipids, predominantly globotriaosylceramide (Gb3). A transgenic mouse expressing the human α-Gal A R301Q mutant in an α-Gal A-knockout background (TgM/KO) should be useful for studying active-site-specific chaperone (ASSC) therapy for Fabry disease. However, the Gb3 content in the heart tissue of this mouse was too low to detect an ASSC-induced effect. To increase the Gb3 levels in mouse organs, we created transgenic mice (TgG3S) expressing human α1,4-galactosyltransferase (Gb3 synthase). High levels of Gb3 were observed in all major organs of the TgG3S mouse. A TgG3S (+/−)M(+/−)/KO mouse was prepared by cross-breeding the TgG3S and TgM/KO mice and the Gb3 content in the heart of the TgG3S(+/−)M(+/−)/KO mouse was 1.4 µg/mg protein, higher than in the TgM(+/−)/KO (<0.1 µg/mg protein). Treatment with an ASSC, 1-deoxygalactonojirimycin, caused a marked induction of α-Gal A activity and a concomitant reduction of the Gb3 content in the TgG3S(+/−) M(+/−)/KO mouse organs. These data indicated that the TgG3S(+/−) M(+/−)/KO mouse was suitable for studying ASSC therapy for Fabry disease, and that the TgG3S mouse would be useful for studying the effect of high Gb3 levels in mouse organs