OBJECTIVETo investigate the distribution pattern of the Secretion complex in Streptococcus mutans by means of the subcellular localization of SecA and SecY.

METHODSThe specificity of anti-SecA antibody and the anti-SecY antibody were examined by Western blot. An indirect postembedding immunogold method was used to determine the subcellular localization of the SecA and SecY in the cytoplasmic membrane of the Streptococcus mutans GS-5.

RESULTSImmunoblotting results showed that the anti-SecA antibody and the anti-SecY antibody specifically recognized a single band of about 95 000 and 47 800 respectively. Immunogold electron microscopy revealed a single intense focus of gold particles at a discrete location on the cytoplasmic membrane of the Streptococcus mutans GS-5.

CONCLUSIONSSecA and SecY clustered to an asymmetric microdomain, which suggests that Sec complex present a uni-site on the cytoplasmic membrane of Streptococcus mutans.

Adenosine Triphosphatases ; metabolism ; Bacterial Proteins ; metabolism ; Cytoplasm ; metabolism ; Immunohistochemistry ; Membrane Transport Proteins ; metabolism ; SEC Translocation Channels ; Streptococcus mutans ; metabolism

Sec61β, a subunit of the Sec61 translocon complex, is not essential in yeast and commonly used as a marker of endoplasmic reticulum (ER). In higher eukaryotes, such as Drosophila, deletion of Sec61β causes lethality, but its physiological role is unclear. Here, we show that Sec61β interacts directly with microtubules. Overexpression of Sec61β containing small epitope tags, but not a RFP tag, induces dramatic bundling of the ER and microtubule. A basic region in the cytosolic domain of Sec61β is critical for microtubule association. Depletion of Sec61β induces ER stress in both mammalian cells and Caenorhabditis elegans, and subsequent restoration of ER homeostasis correlates with the microtubule binding ability of Sec61β. Loss of Sec61β causes increased mobility of translocon complexes and reduced level of membrane-bound ribosomes. These results suggest that Sec61β may stabilize protein translocation by linking translocon complex to microtubule and provide insight into the physiological function of ER-microtubule interaction.
Animals ; COS Cells ; Caenorhabditis elegans Proteins ; genetics ; metabolism ; Cell Line, Tumor ; Cercopithecus aethiops ; Endoplasmic Reticulum ; metabolism ; Homeostasis ; Humans ; Microtubules ; metabolism ; SEC Translocation Channels ; deficiency ; genetics ; metabolism