N-terminal variants

Deamidated forms Methionine sulfoxides Proteolytically clipped forms N-Terminal variants Disulfide isomers... 

N-terminal variants, glycosylation variants, disulfide isomers, proteolytic clips Dimers/aggregates... 

Deamidated forms, N-terminal variants, proteolytic clips... 

C. Detection of N-terminal Variants Using Peptide Mapping and Fluorescence Detection... 

The problem of N-terminal variants in recombinant proteins is not uncommon. E. coli synthesizes proteins with a formylated methionine at the N terminus. In vivo, E. coli often removes N-formyl methionine with the action of a deformylase followed by methionine amino peptidase. This removal is not always exact and neighboring amino acids in the peptide chain influence the removal.130 This can yield recombinant products lacking a number of encoded amino acids at the N terminus. For smaller proteins, these product-related impurities generally are detected and quantitated by RP-HPLC. However, large proteins differing by only one or two N-terminal amino acids may be difficult to resolve by RP-HPLC. In these instances, peptide mapping by RP-HPLC is a valuable tool. 

Sjoberg, M., Vennstrom, B. Forrest, D. (1992). Thyroid hormone receptors in chick retinal development dififierential expression of mRNAs for a and N-terminal variant receptors. Development, 114, 39-47. 

Fleischhauer, K., Park, J H, DiSanto, J. P., Marks, M, Ozato, K., and Yang, S Y (1992) Isolation of a full-length cDNA clone encoding a N-terminally variant form of the human retinoid X receptor p. Nucleic Acids Res. 20, 1801. 

Crofts LA, Hancock MS, Morrison NA, Eismann JA (1998) Multiple promoters direct the tissue-specific expression of novel N-terminal variant human vitamin D receptor gene transcripts. Proc Natl Acad Sci USA 95 10529... 

AMP-activated Protein Kinase. Table 1 Information about subunit isoforms of AMP-activated protein kinase. Data refer to the full-length forms of the human isoforms. The y2 and y3 isoforms also exist as splice variants that are N-terminal truncations, with lower molecular mass and number of amino acids (38 kDa and 328 amino acids for the short form of y2, 52 kDa and 464 amino acids for the short form of y3). Other splice variants may also exist... 

ECEs are metalloproteinases that are homologous to the neutral endopeptidase (NEP, E-24.11, neprilysin) unlike NEP, however, they form disulfide-bonded homodimers. In man, with ECE-1 and ECE-2, two isoforms are known, which are encoded by two separate genes. For ECE-1 four different variants have been identified (ECE-1 a-d), which are generated by the use of alternative promoters (Table 2). The ECE-1 isoforms only differ in their N-terminal amino acid sequence. For ECE-2, a single gene product has been described in... 

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