Ancestral gene

Homology between PemA and PemB is quite low (19). Thus, it seems unlikely that the presence in E. chrysanthemi of two pern genes results firom a recent duplication of an ancestral gene as proposed for pel genes. The six regions conserved in bacterial or plant pectin methylesterases are present in PemA and PemB (19, 21). Since the central regions II, III, IV and V are more conserved than regions I and VI, they are more probable candidates to be involved in the catalytic site. 

MAO A and B differ in primary structure and in substrate specificity [5,7]. The two isozymes, located on the mitochondrial outer membranes, have 70% homology in peptide sequence and share common mechanistic details. It is now recognized that these are different proteins encoded by different genes, but probably derived from a common ancestral gene. Crystal structures for both MAO A and B complexes with inhibitors have recently been reported [8]. Serotonin is selectively oxidized by MAO A, whereas benzylamine and 2-phenylethylamine are selective substrates for MAO B. Dopamine, norepinephrine, epinephrine, trypt-amine, and tyramine are oxidized by both MAO A and B in most species [9]. In addition, MAO A is more sensitive to inhibition by clorgyline (1), whereas MAO B is inhibited by low concentrations of L-deprenyl ((f )-( )-deprenyl) (2) [5,6cj. Development of inhibitors that are selective for each isozyme has been an extremely active area of medicinal chemistry [8]. 

Evolution of moth sex pheromones via ancestral genes. Proceedings of the National Academy of Sciences, USA99 13621-13626. 

The receptor for insulinlike growth factor-1 (IGF-1) is also similar to the insulin receptor in structure and tyrosine kinase activity. Thus, in this case it is likely that the hormones (insulin and IGF-1) and their receptors have each evolved from common ancestral genes by duplication and divergence. 

What will we gain from structural and mechanistic data on the / -(l- 4) glycoside hydrolases First, we will be able to identify evolutionary pathways of these enzymes and determine whether they originated from the same ancestral gene or whether there are several distinctly different classes. Second, it may be possible to modify the enzymes more... 

Domain II is composed of two subdomains (Ha and lib) and represents the catalytic core of the protease. A cys at position 115 (p,-calpain) or 105 (m-calpain), a His residue at position 272 ((x-calpain) or 262 (m-calpain) and an Asn residue at position 296 ( x-calpain) or 286 (m-calpain) form the catalytic triad characteristic of cysteine proteases such as papain or cathepsins B, L, or S. Domain II, however, shares only limited sequence homology with other cysteine proteases, and is likely to have evolved from a different ancestral gene. 

Gelsolin itself was discovered in 1979 by Yin and Stossel based on its ability to activate the gel-sol transformation of actin filaments in a calcium-dependent manner (Yin and Stossel, 1979 Yin et al., 1980). Gelsolin is composed of six domains, named S1-S6, that appears to have arisen from triplication, followed by duplication of an ancestral gene encoding a single domain protein of about 15 kDa (Kwiatkowski et al., 1986) (see Figure 2 Gelsolin structure). 

III. p-DECARBOXYLATING DEHYDROGENASES HAVE EVOLVED DIVERGENTLY FROM A COMMON ANCESTRAL GENE... 

The parallels among chitin, cellulose, and HA structures, all being j3 -chains of hexose polymers are reflected in the striking similarity in sequence between the HAS from vertebrates, cellulose synthases from plants, and chitin synthases from fungi. A primordial ancestral gene must have existed from which all of these enzymes evolved that are involved in the biosynthesis of all polymers that contain -glycoside linkages, an ancient j3-polysaccharide synthase. 

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