Protein sequencing gene duplication

Most sequences belong to multigene families. These are proteins that have evolved by gene duplication, usually followed by specialization of function. There will be a group of homologous proteins, all of which... 

Proteins containing two 4Fe 4S clusters, typified by the P. aerogenes ferredoxin (PaFd), show striking sequence similarities between the amino- and carboxy-terminal halves of the molecule, suggesting that these proteins evolved by gene duplication of a more primitive protein (Section I,E,3). Of particular note is the pattern of four cysteines in the two halves of the molecule (Cys-8, -11, -14, -18 and Cys-35, -38, -41, -45 in the amino- and carboxyl-terminal halves, respectively, of the PaFd se-... 

The three molecules of the IL-1 family, interleukin-la (IL-la), interleukin-1 3 (IL-ip), and interleukin-1 receptor antagonist (IL-IRa) map to the long arm of chromosome two in the human genome. It appears that the family arose via a gene duplication event some 350 million years ago, and the molecules possess between 27.5 and 36% sequence identity with each other (Table 2) [1,14,15]. In addition, the genes for the two IL-1 receptors IL-1R1 and IL-1RII [16,17], and an IL-1R accessory protein (IL-lRacP), which binds to the IL-1, IL-1 receptor complex [18], have been identified. Together, these molecules via their differential activity serve primarily to modulate the host defense mechanism. 

The amino acid sequence of a protein not only reveals the primary structure of the protein but also information on possible protein families or groups and evolutionary relationships, potential gene duplication(s) and possible post-translational modifications. In addition, a knowledge of the amino acid sequence can be used to generate specific antibodies and DNA probes. 

The presence of repeating stretches of sequence would indicate that the protein may have arisen by gene duplication (e.g. in antibody molecules see Topic D2). 

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