In general, transferases catalyze the transfer of one molecular group from one molecule to another. For instance, such molecular groups include phosphate, amino, methyl, acetyl, acyl, phosphatidyl, phosphoribosyl, among other groups. One particular transferase, fucosyltransferase, transfers a fucosyl group from one molecule to another.
Fucosyltransferases catalyze the transfer of fucose from GDP-Fuc to Gal in an α1,2-linkage and to GlcNAc in an α1,3-, α1,4-, or α1,6-linkage. Since known fucosyltransferases utilize the same nucleotide sugar, it is believed that their specificity resides in the recognition of the acceptor and in the type of linkage formed. On the basis of protein sequence similarities, these enzymes have been classified into four distinct families: (1) the alpha-2-fucosyltransferases, (2) the alpha-3-fucosyltransferases, (3) the mammalian alpha-6-fucosyltransferases, and (4) the bacterial alpha-6-fucosyltransferases. Conserved structural features, as well as a consensus peptide motif have been identified in the catalytic domains of all alpha-2 and alpha-6-fucosyltranferases, from prokaryotic and eukaryotic origin. Based on these sequence similarities, alpha-2 and alpha-6-fucosyltranferases have been grouped into one superfamily. In addition, a few amino acids were found strictly conserved in this superfamily, and two of these residues have been reported to be essential for enzyme activity for a human alpha-2-fucosyltransferase. The alpha-3-fucosyltransferases constitute a distinct family as they lack the consensus peptide, but some regions display similarities with the alpha-2 and alpha-6-fucosyltranferases. All these observations strongly suggest that the fucosyltransferases share some common structural and/or catalytic features.
Fucosyltransferases are thought to be involved in the synthesis of ABO blood group antigens and in tumor cell adhesion, among other physiological phenomena. See, e.g., Koda et al. (1997) J. Biol. Chem. 272:7501-7505; and Weston et al. (1999) Cancer Res. 59:2127-2135. For example, α(1,2)fucosyltransferase forms the H blood group antigen and catalyzes the transfer of fucose in the α(1,2) linkage to the terminal galactose of a precursor molecule. In addition, facosyltransferases have been found to be associated with particular mucins, the coregulation of which is lost in gastric tumors in comparison to normal gastric epithelial cells. Lopez-Ferrer, A., et al. (2000) Gut 47(3):349-56.
Given the important biological roles and properties of fucosyltransferases, there exists a need for the identification and characterization of novel fucosyltransferase genes and proteins as well as for the discovery of binding agents (e.g., ligands) and modulators of these nucleic acids and polypeptides for use in regulating a variety of normal and/or pathological cellular processes.
G-protein coupled receptors (GPCRs) are proteins that mediate signal transduction of a diverse number of ligands through heterotrimeric G proteins (see, e.g., Strader (1994) Annu. Rev. Biochem. 63:101-132). GPCRs are a component of many modular cell signaling systems involving, e.g., G proteins, intracellular enzymes and channels. Upon ligand binding to a GPCR, intracellular signal molecules, e.g., G proteins, can be activated or turned off. These GPCR-coupled G proteins can modulate the activity of different intracellular effector molecules, e.g., enzymes and ion channels (see, e.g., Gutkind (1998) J. Biol. Chem. 273: 1839-1842; Selbie (1998) Trends Pharmacol. Sci. 19:87-93).
GPCR polypeptides typically include seven transmembrane domains, including an intracellular domain and an extracellular ligand binding domain. The intracellular domain(s) bind G proteins, which represent a family of heterotrimeric proteins comprising of α, β and γ subunits. G proteins typically bind guanine nucleotides. Following ligand binding to the GPCR, a conformational change is transmitted from the extracellular GPCR ligand binding domain to the intracellular domain-bound G protein. This causes the G protein α-subunit to exchange a bound GDP molecule for a GTP molecule and to dissociate from the βγ-subunits. The GTP-bound form of the α-subunit typically functions as an effector-modulating moiety, leading to the production of second messengers, such as, e.g., cyclic AMP (e.g., by activation of adenylate cyclase), diacylglycerol or inositol phosphates.
GPCRs are of critical importance in cell signaling systems, including the endocrine system, the central nervous system and peripheral physiological processes. The GPCR genes and gene-products can also be causative agents of disease (see, e.g., Spiegel (1993) J. Clin. Invest. 92:1119-1125); McKusick (1993) J. Med. Genet. 30:1-26). Given the important biological roles and properties of GPCRs, there exists a need for the identification and characterization of novel GPCR genes and proteins as well as for the discovery of binding agents (e.g., ligands) and modulators of these nucleic acids and polypeptides for use in regulating a variety of normal and/or pathological cellular processes. Since RAlc may be the cognate receptor for specific endogenous ligand, the 52874 and 52880 proteins may similarly recognize an endogenous ligand.
One type of receptor family is the seven transmembrane domain (7TM) receptor family. This receptor family is characterized structurally by the presence of seven hydrophobic, membrane-spanning regions, as well as an intracellular domain and an extracellular ligand binding domain. Members of the 7TM receptor family typically are G-protein coupled receptors (GPCRs). G-protein coupled receptors are proteins that mediate signal transduction of a diverse number of ligands through heterotrimeric G proteins (see, e.g., Strader (1994) Annu. Rev. Biochem. 63:101-132). GPCRs are a component of many modular cell signaling systems involving, e.g., G proteins, intracellular enzymes and channels. Upon ligand binding to a GPCR, intracellular signal molecules, e.g., G proteins, can be activated or turned off. These GPCR-coupled G proteins can modulate the activity of different intracellular effector molecules, e.g., enzymes and ion channels (see, e.g., Gutkind (1998) J. Biol. Chem. 273: 1839-1842; Selbie (1998) Trends Pharmacol. Sci. 19:87-93).
The intracellular domain(s) of GPCRs bind G proteins, which represent a family of heterotrimeric proteins comprising of α, β and γ subunits. G proteins typically bind guanine nucleotides. Following ligand binding to the GPCR, a conformational change is transmitted from the extracellular GPCR ligand binding domain to the intracellular domain-bound G protein. This causes the G protein α-subunit to exchange a bound GDP molecule for a GTP molecule and to dissociate from the βγ-subunits. The GTP-bound form of the α-subunit typically functions as an effector-modulating moiety, leading to the production of second messengers, such as, e.g., cyclic AMP (e.g., by activation of adenylate cyclase), diacylglycerol or inositol phosphates.
Seven TM receptors, such as GPCRs, are of critical importance in cell signaling systems, including the endocrine system, the central nervous system and peripheral physiological processes. GPCRs are the receptors of different families of neuropeptides, and neuropeptides are involved in nociception. The GPCR genes and gene-products can also be causative agents of disease (see, e.g., Spiegel (1993) J. Clin. Invest. 92:1119-1125); McKusick (1993) J. Med. Genet. 30:1-26). Given the important biological roles and properties of 7TMs, there exists a need for the identification and characterization of novel 7TM genes and proteins as well as for the discovery of binding agents (e.g., ligands) and modulators of these nucleic acids and polypeptides for use in regulating a variety of normal and/or pathological cellular processes.
Members of the Rho family of small G proteins transduce signals from plasma-membrane receptors and control cell adhesion, motility and shape by actin cytoskeleton formation. Like all other GTPases, Rho proteins act as molecular switches, with an active GTP-bound form and an inactive GDP-bound form. The active conformation is promoted by guanine-nucleotide exchange factors, and the inactive state by GTPase-activating proteins (GAPs) which stimulate the intrinsic GTPase activity of small G proteins. GAPs promote GTP hydrolysis, which switches the G-protein to the inactive state.
RhoGAP domains are found in a wide variety of large, multi-functional proteins. Barrett, T., et al. (1997) Nature 385(6615):458-61. A number of structures are known for this family. Please see Musacchio, A., et al. (1996) Proc Natl Acad Sci 93(25):14373-8; Rittinger, K., et al. (1997) 388(6643):693-7; and Boguski, M. S., et al. (1993) Nature 366(6456):643-54, all of which are incorporated herein by reference. The RhoGAP domain is composed of several alpha helices. This domain is also known as the breakpoint cluster region-homology (BH) domain. In addition to their GAP domains, the rhoGAP proteins may contain SH2, SH3, Ser/Thr kinase, and pleckstrin homology domains as well as proline-rich regions. Several of these domains are known to mediate protein-protein interactions. With the exception of the chimerins that are found in the brain, rhoGAPs are ubiquitously expressed and so require tight regulation to prevent permanent deactivation of Rho-family GTPases. The coupling of protein-protein interaction domains to rhoGAP activity probably provides an indirect means of regulation through control of its subcellular location.
Given the important biological roles and properties of rhoGAPs, there exists a need for the identification and characterization of novel rhoGAP genes and proteins as well as for the discovery of binding agents (e.g., ligands) and modulators of these nucleic acids and polypeptides for use in regulating a variety of normal and/or pathological cellular processes.