Protein translocation, endoplasmic reticulum membrane

Kuroiwa, T., Sakaguchi, M., Mihara, K., and Omura, T. (1991). Systematic analysis of stop-transfer sequence for microsomal membrane. Biol. Chem. 266, 9251—9255. Kuroiwa, T., Sakaguchi, M., Omura, T., and Mihara, K. (1996). Reinitiation of protein translocation across the endoplasmic reticulum membrane topogenesis of multispan-ning membrane proteins. J. Biol. Chem. 271, 6243—6248. 

Blobel discovered the mechanism for protein translocation across the endoplasmic reticulum membrane—the signal hypothesis. 

RNA polymerase III (RNA Pol III) is also located in the nucleoplasm. It transcribes the genes for tRNA, 5S rRNA, U6 snRNA, and the 7S RNA associated with the signal recognition particle (SRP) involved in the translocation of proteins across the endoplasmic reticulum membrane (see Topic H4). 

Nilsson, I., Witt, S., Kiefer, H., Mingarro, I., and von Heijne, G. (2000). Distant downstream sequence determinants can control N-tail translocation during protein insertion into the endoplasmic reticulum membrane./. Biol. Chem. 275, 6207-6213. 

Signal Sequences Mark Proteins for Translocation Across the Endoplasmic Reticulum Membrane... 

Rapoport, T. A., K. E. Matlack, K. Plath, B. Misselwitz, and O. Staeck. 1999. Post-translational protein translocation across the membrane of the endoplasmic reticulum. Biol. Chem. 380 1143-1150. 

Gillece P, Pilon M, Romisch K (2000) The protein translocation channel mediates glycopeptide export across the endoplasmic reticulum membrane. Proc Natl Acad Sci USA 97 4609 -4614 Ginsberg HN (1997) Role of lipid synthesis, chaperone proteins and proteasomes in the assembly and secretion of apoprotein B-containing lipoproteins from cultured liver cells. Clin Exp Pharmacol Physiol 24 A29-A32... 

Kalies KU, Allan S, Sergeyenko T et al. (2005) The protein translocation channel binds proteasomes to the endoplasmic reticulum membrane. EMBO J 24(13), 2284-2293. 

Krieg, U.C., Johnson, A.E., and Walter, R, Protein translocation across the endoplasmic reticulum membrane identification by photocross-Hnking of a 39-kD integral membrane glycoprotein as part of a putative translocation tunnel, /. Cell Biol., 109, 5, 2033, 1989. 

Walter, P., and Blobel, G. (1981a). Translocation of proteins across the endoplasmic reticulum III. Signal recognition protein (SRP) causes signal sequence-dependent and site-specific arrest of chain elongation that is released by microsomal membranes. J. Cell Biol. 91, 557-561. 

The site of synthesis of numerous proteins is remote from their site of function. During transfer from one site to the other, proteins must, therefore, cross cellular membranes [43] [44], Proteins are usually synthesized as precursors containing an amino terminal extension, called the signal (leader) peptide, the sequence of which contains the necessary information to guide the protein to and across a specific membrane. After transmembrane transport (called translocation), the signal peptide is cleaved off by specific signal peptidases, which are found in the rough endoplasmic reticulum, and the... 

The phosphatidylcholine in bile is synthesised in the endoplasmic reticulum of the hepatocyte and must be transported to the canalicular membrane. One possibility involves the nonspecific phosphatidylcholine transfer protein but a mouse null for this protein did not show reduced phosphatidylcholine secretion into bile and there was no compensatory increase in other phospholipids transfer proteins. However, the plasma membrane would receive a ready supply of phospholipid by insertion of vesicles, and the MDR3 protein translocates this molecule from the inner leafiet to the outer surface where there is contact with bile acids, as suggested by Smit and colleagues. The role of this transporter is shown in Figure 2.2. 

Hagting A, Karlsson C, Clute P, Jackman M, Pines J (1998) MPF localization is controlled by nudear export. EMBO J 17 4127-4138 Hamman BD, Chen JC, Johnson EE, Johnson AE (1997) The aqueous pore through the translocon has a diameter of 40-60 A during cotranslational protein translocation at the ER membrane. Cell 89 535-544 Hampton RY, Rine J (1994) Regulated degradation of HMG-CoA reductase, an integral membrane protein of the endoplasmic reticulum, in yeast. J Cell Biol 125 299-312... 

A variety of other calcium transport systems are associated with Ca21-activated ATPases. The extraembryonic structure, the chorioallantoic membrane, of the chick embryo is responsible for the translocation of over 120 mg of eggshell calcium into (he embryo during development. The enzyme responsible for this is a (Ca2+, Mg2+)-ATPase with Km values for Ca2+ of 30 p,mol dm-3 and 0.3 mmol dm-3, and a molecular weight of 170 000. The enzyme can be crossiinked and co-isolated with a calcium-binding protein.158 Transport of Ca2+ is also associated with (Ca2+, Mg2+)-ATPases in neutrophil plasma membranes,159 transverse tubule membranes from rabbit skeletal muscle,160 rabbit myocardial membrane,161 endoplasmic reticulum,162 sar-colemma,163 brain microsomes,164 the Golgi apparatus165 and rat liver plasma membranes.166... 

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