Amino-acid sequence alteration

Given a large population of individuals, a considerable number of sequence variants can be found for a protein. These variants are a consequence of mutations in a gene (base substitutions in DNA) that have arisen naturally within the population. Gene mutations lead to mutant forms of the protein in which the amino acid sequence is altered at one or more positions. Many of these mutant forms are neutral in that the functional properties of the protein are unaffected by the amino acid substitution. Others may be nonfunctional (if loss of function is not lethal to the individual), and still others may display a range of aberrations between these two extremes. The severity of the effects on function depends on the nature of the amino acid substitution and its role in the protein. These conclusions are exemplified by the more than 300 human... 

Single-base substitutions, which affect the amino acid sequence of proteins and lead to altered protein function, are the most frequent type of polymorphisms associated with many disease phenotypes as well as with variation in drag response... 

Many of the initial biopharmaceuticals approved were simple replacement proteins (e.g. blood factors and human insulin). The ability to alter the amino acid sequence of a protein logically coupled to an increased understanding of the relationship between protein structure and function (Chapters 2 and 3) has facilitated the more recent introduction of several engineered therapeutic proteins (Table 1.3). Thus far, the vast majority of approved recombinant proteins have been produced in the bacterium E. coli, the yeast S. cerevisiae or in animal cell lines (most notably Chinese hamster ovary (CHO) cells or baby hamster kidney (BHK) cells. These production systems are discussed in Chapter 5. 

Weinshilboum R, Wang L. Pharmacogenetics Inherited variation in amino acid sequence and altered protein quantity. Clin Pharmacol Ther 2004 75(4) 253-258. 

Almost all membrane proteins have their own topology that is uniquely determined by its amino acid sequence information. However, some exceptional proteins have dual orientations (Dunlop et al., 1995). In another protein, the orientation is altered in vivo for functional reasons (Bruss et al., 1994 Prange and Streeck, 1995). The molecular mechanisms of the topogenesis of membrane proteins are not fully understood, but some important findings are described next. 

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