General insertion protein

Voltage-gated potassium (Kv) channels are membrane-inserted protein complexes, which form potassium-selective pores that are gated by changes in the potential across the membrane. The potassium current flow through the open channel follows by the electrochemical gradient as defined by the Nernst equation. In general, Kv channels are localized in the plasma membrane. 

The Rieske protein in mitochondrial bci complexes is assembled when the protein is incorporated into the complex. The Rieske protein is encoded in the nucleus and synthesized in the cytosol with a mitochondrial targeting presequence, which is required to direct the apoprotein to the mitochondrial matrix. The C-terminus is then targeted back to the outside of the inner mitochondrial membrane where the Rieske cluster is assembled. In addition, the presequence is removed and the protein is processed to its mature size after the protein is inserted into the bci complex. In mammals, the presequence is cleaved in a single step by the core proteins 1 and 2, which are related to the general mitochondrial matrix processing protease (MPP) a and (3 subunits the bovine heart presequence is retained as a 8.0 kDa subunit of the complex (42, 107). In Saccharomyces cerevis-iae, processing occurs in two steps Initially, the yeast MPP removes 22 amino acid residues to convert the precursor to the intermediate form, and then the mitochondrial intermediate protease (MIP) removes 8 residues after the intermediate form is in the bci complex (47). Cleavage by MIP is independent of the assembly of the Rieske cluster Conversion of the intermediate to the mature form was observed in a yeast mutant that did not assemble any Rieske cluster (35). However, in most mutants where the assembly of the Rieske cluster is prevented, the amount of Rieske protein is drastically reduced, most likely because of instability (35, 44). 

There are many cellular membranes, each with its own specific features. No satisfactory scheme describing the assembly of any one of these membranes is available. How various proteins are initially inserted into the membrane of the ER has been discussed above. The transport of proteins, including membrane proteins, to various parts of the cell inside vesicles has also been described. Some general points about membrane assembly remain to be addressed. 

It has been shown that the half-lives of the lipids of the ER membranes of rat liver are generally shorter than those of its proteins, so that the turnover rates of lipids and proteins are independent. Indeed, different lipids have been found to have different half-Eves. Furthermore, the half-lives of the proteins of these membranes vary quite widely, some exhibiting short (hours) and others long (days) half-lives. Thus, individual lipids and proteins of the ER membranes appear to be inserted into it relatively independently this is the case for many other membranes. 

Members of this family of molecules may have only one Ig-like domain, as is the case for the myelin protein P0, or, as for most of the family, have many Ig domains. In addition to the subclassification of Ig domains into V-, C- and C2-like domains, Ig family members can be broadly divided into three general classes [8] (a) those that have only Ig-like domains (b) those that have Ig domains and additional domains that resemble regions of the ECM component fibronectin, termed FN-like domains and (c) those that have Ig domains and motifs other than FN-like domains. Moreover, any one Ig family member may have many isoforms, which may differ in the length of the cytoplasmic domain, in their post-translational modifications and whether they are membrane-spanning or glycosylphos-phatidylinositol (GPI)-anchored proteins (see Box 3-1). Also, additional amino acid sequences inserted in the extracellular domain may distinguish isoforms of a particular IgCAM. While it is not known how the majority... 

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