Principles of Protein Structure - G. Schultz 1982

Structural basis of protein mechanism, action, and function
Biological and medical aspects of protein action and function
Evolution of novel functions from preexisting proteins

Cell/13.html">Protein Structure can be significantly older than its function. Lactalbumin, for instance, which emerged as a functional component of the Mammary Glands about 100 million years ago, likely existed as a Lysozyme-like protein long before The Need for this specific function arose. Apparently, any thermodynamically feasible function can evolve on The basis of pre-existing protein structures (cf. Section 9.3).

A novel function can also evolve from precursor Proteins in a completely new functional direction [754]. As can be seen from Table 9.4, Serine protease serves as a prototype of a functional unit that has been repeatedly recruited during the evolution of complex physiological systems. Another common example is the proteins Actin and Myosin, which are widely distributed in motile Cells and their contents [755, 756]. In higher organisms, actin-myosin systems drive such diverse Functions as Muscle contraction, the release of Neurotransmitters in The Nervous system, the amoeboid movement of white Blood Cells, and the sealing of damaged Blood Vessels through clot formation. Furthermore, in certain biological processes where cell shape must be stabilized or altered, the ability of actin to form highly diverse structures via reversible polymerization is brought into play [757].

The fact that A wide variety of functions is not accompanied by a similarly vast variety of structures [586] holds positive implications for practical medicine, as it demonstrates that molecular physiology may not be as inscrutable as was once believed until recently. However, this positive aspect remains vastly underutilized because structurally specific drugs, such as serine protease inhibitors or acetylsalicylate, can elicit a wide range of diverse effects and thus lack selectivity [84].