Post-translational modification. See

Nucleophilic attack by the amino group of the neighbouring aminoacyl thioester is catalysed by the C domain, and this results in amide (peptide) bond formation. Enzyme-controlled biosynthesis in this manner is a feature of many microbial peptides, especially those containing unusual amino acids not encoded by DNA and where post-translational modification (see Section 13.1) is unlikely. 

The precursor molecule of collagen (preprocollagen), formed in the rER, is subject to extensive post-translational modifications (see p. 232) in the ER and Golgi apparatus. 

Hydrophilic hormones and other water-soluble signaling substances have a variety of biosynthetic pathways. Amino acid derivatives arise in special metabolic pathways (see p. 352) or through post-translational modification (see p. 374). Proteohormones, like all proteins, result from translation in the ribosome (see p. 250). Small peptide hormones and neuropeptides, most of which only consist of 3-30 amino acids, are released from precursor proteins by proteolytic degradation. 

Here, we describe approaches for utilizing recombinant TPST-1 and TPST-2 to enzymatically sulfate N-terminal chemokine receptor peptides and for the characterization of these sulfopeptides. For a more expansive introduction to TPST enzymes and proteins containing sulfotyrosine post-translational modifications, see the following references Ludeman and Stone (2014), Moore (2003, 2009), Seibert and Sakmar (2008), and Stone, Chuang, Hou, Shoham, and Zhu (2009). 

Transit peptides amino-terminal extensions of precursors to chloroplast proteins which are encoded by nuclear DNA and synthesized in the cytoplasm. The T.p. are removed by Post-translational modification (see) before the protein takes on its mature configuration inside the chloroplast. The overall amino acid sequences of the T.p. are not conserved between species, but the positions of proline and the charged amino acids are highly conserved. The T.p. appear to mediate transport of the chloroplast protein precur-... 

Yeast. The advantages of expression in yeast include potentially high level production of proteins, the abiUty to have expressed proteins secreted into the media for ease of purification, and relatively low cost, easy scale-up. A disadvantage is that plasmid instabiUty may be a problem which can lead to low product yield. Whereas post-translational modification occurs in yeast, proteins are quite often hyperglycosylated. This is generally a problem with expression in Saccharomyces cerevisiae but not for the more recently used yeast host Pichiapastoris (25) (see Yeasts). 

MammaBan. For mammalian proteins, mammalian cells offer the most natural host for expression. Problems of incorrect processing and post-translational modification are avoided using these cells. Mammalian cells are usually grown in continuous cell culture, reducing the variabiUty in results (see Cell CULTURE technology). Moderate-level production of native protein is possible. The procedure, however, is slow and very cosdy, and the level of protein expression is low. Thus large-scale production of proteins in mammalian cells is not practical. When low quantities of protein are sufficient, this system offers the several advantages described. 

Another form of post-translational modification that may add carbohydrate to a polypeptide is non-enzymatic glycation. This reaction occurs between the reducing ends of sugar molecules and the amino groups of proteins and peptides. See Section 2.1 in this chapter for further details and the reaction sequence behind this modification. 

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... 

In addition to containing protein-protein interaction motifs, E3-substrate specificity may be affected by post-translational modifications. In particular, phosphorylation can alter E3-substrate interactions. One example is p53 where certain phosphorylations inhibit its direct binding to Mdm2, while others indirectly enhance their association by promoting nuclear localization of p53 [104-106]. Phosphorylation also directly enhances substrate interactions, as exemplified by the Cbls, which include phospho-tyrosine binding domains (see below) [107]. 

Histone acetylation is without a doubt one of the most thoroughly characterized post-translational modifications of histones where both the functional (see Section 3.1) and structural implications for chromatin have been explored. In the sections that follow we are going to summarize the major structural effects of this post-translational modification as they pertain to the nucleosome and the chromatin fiber. 

A true appreciation of the subtle and complex ways in which the nucleosome can influence gene expression, has come only recently, largely through studies of the post-translational modifications to which all histones are subject and of the enzymes that add and remove these modifications. It has been known for many years that the histone N-terminal tails are exposed on the surface of the nucleosome and that selected amino acid residues are subject to a variety of enzyme-catalyzed, post-translational modifications. These include acetylation of lysines, phosphorylation of serines, and methylation of lysines and arginines ([6,7], see also chapters by Davie, and Ausio and Abbott, this volume). The locations of the histone N-terminal tails in the nucleosome and the residues that can be modified are shown in Fig. 1. 

A further post-translational modification of p53 is an acetylation at the C terminus, for which stimulation of specific DNA binding has been reported (Wei and Roeder, 1997). Possibly, this acetylation is mediated by the CBP/p300 proteins (see 1.4.6), with which the p53 protein can specifically interact. 

The prenyl transferases are a class of enzymes that is involved in post-translational modification of membrane-associated proteins. These enzymes catalyze the transfer of a farnesyl (FTase, EC 2.5.1.58, for structural information see References 55-65) or geranyl-geranyl group (GGTase I, EC 2.5.1.59 GGTase n, EC 2.5.1.60, for structural information... 

The proteins of milk fall into several classes of polypeptide chains. These have been delineated most completely in bovine milk, and a system of nonmenclature has been developed for them (Chapter 3 Eigel et al. 1984). One group, called caseins, consists of four kinds of polypeptides asr, as2-. and 3-, and k- with some genetic variants, post translational modifications, and products of proteolysis. Almost all of the caseins are associated with calcium and phosphate in micelles 20-300 fim in diameter (see Chapter 9). The other milk proteins, called whey proteins, are a diverse group including /3-lactoglobulin, a-lactalbumin, blood serum albumin, and immunoglobulins (Chapter 3). Almost all... 

All plants contain a PEPCase enzyme which, among other likely roles (Vidal et al., 1986), serves to replenish tricarboxylic acid cycle intermediates that are consumed during ammonium assimilation (Latzko Kelly, 1983). The role of this enzyme, other than its presumed housekeeping function, has not been studied in any detail and its activity is probably not controlled by environmental factors. Isoforms of PEPCase have been observed in many plants (C3, C4 and CAM) for example, in rice five isoforms have been detected immunologically and in most plants two to four bands that react with anti-PEPCase antibodies are found (Matsuoka Hata, 1987). It is not clear how these isoforms arise, e.g. by post-translational modification of one form, or whether all of these forms are products of different genes. The housekeeping-type PEPCase enzyme, concerned with anaplerotic functions, is distinct from other PEPCase enzymes that function in plants with C4 and CAM metabolism (see below). 

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