Evolution, protein families

Using a protein family to explore evolution requires the identification of family members with similar molecular functions in the widest possible range of organ-... 

Many examples of recurring domain or motif structures are available, and these reveal that protein tertiary structure is more reliably conserved than primary sequence. The comparison of protein structures can thus provide much information about evolution. Proteins with significant primary sequence similarity, and/or with demonstrably similar structure and function, are said to be in the same protein family. A strong evolutionary relationship is usually evident within a protein family. For example, the globin family has many different proteins with both structural and sequence similarity to myoglobin (as seen in the proteins used as examples in Box 4-4 and again in the next chapter). Two or more families with little primary sequence similarity sometimes make use of the same major structural... 

Structural motifs become especially important in defining protein families and superfamilies. Improved classification and comparison systems for proteins lead inevitably to the elucidation of new functional relationships. Given the central role of proteins in living systems, these structural comparisons can help illuminate every aspect of biochemistry, from the evolution of individual proteins to the evolutionary history of complete metabolic pathways. 

Christophides G. K., Mintzas A. C. and Komitopoulou K. (2000) Organization, evolution and expression of a multigene family encoding putative members of the odourant binding protein family in the medfly Ceratitis capitata. Insect Mol. Biol. 9, 185-195. 

Before the evolution of protein function can be studied, functional differences first must be demonstrated between members of the family. At present, the best comparative biochemical data exist for classically studied protein families, such as the globin family and several families of digestive enzymes.3... 

Other proteins crucial to signal-transduction pathways arose much later. For example, the eukaryotic protein kinases are one of the largest protein families in all eukaryotes and yet appear to be absent in prokaryotes. The evolution of the eukaryotic protein kinase domain appears to have been an important biochemical step in the appearance of eukaryotes and the subsequent development of multicellular organisms. 

The P propeller domain is a widespread protein organizational motif. Typically, p-propeller proteins are encoded by repeated sequences where each repeat unit corresponds to a twisted P-sheet structural motif these P-sheets are arranged in a circle around a central axis to generate the p-propeller structure. Two superfamilies of P-propeller proteins, the WD-repeat and Kelch-repeat families, exhibit similarities not only in struaure, but, remarkably, also in the types of molectdar functions they perform. Whde it is unlikely that WL) and Kelch repeats evolved from a common ancestor, their evolution into diverse families of similar function may reflect the evolutionary advantages of the stable core P-propeller fold. In this chapter, we examine the relationships between these two widespread protein families, emphasizing recently published work relating to the structure and funrtion of both Kelch and WD-repeat proteins. 

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