Taxonomic distribution of proteins containing GuKc domains

The GuKc domain within your query sequence starts at position 658 and ends at position 837, and its E-value is 7.7e-76.

nArgBP2, a novel neural member of ponsin/ArgBP2/vinexin family that interacts with synapse-associated protein 90/postsynaptic density-95-associated protein (SAPAP).

Kawabe H, Hata Y, Takeuchi M, Ide N, Mizoguchi A, Takai Y
J Biol Chem. 1999; 274: 30914-8

Postsynaptic density (PSD)-95/synapse-associated protein (SAP) 90 and synaptic scaffolding molecule (S-SCAM) are synaptic membrane-associated guanylate kinases. Both the proteins interact with SAP90/PSD-95-associated protein (SAPAP) (also called guanylate kinase-associated protein/Dlg-associated protein). SAPAP is a protein highly enriched in the PSD fraction and may link PSD-95/SAP90 and S-SCAM to Triton X-100-insoluble structures. We found here a novel SAPAP-interacting protein, which was specifically expressed in neural tissue and was present in the postsynaptic density fraction in brain. This protein had a sorbin homology domain in the N terminus, a zinc finger motif in the middle region, and three src homology (SH) 3 domains in the C terminus and was homologous to the ponsin/ArgBP2/vinexin family proteins. We named this protein nArgBP2 because it was the most homologous to ArgBP2. nArgBP2 is a neural member of a growing family of SH3-containing proteins. nArgBP2 bound to the proline-rich region of SAPAP via its third SH3 domain and was coimmunoprecipitated with SAPAP from the extract of rat brain. Furthermore, nArgBP2 was colocalized with SAPAP at synapses in cerebellum. nArgBP2 bound to not only SAPAP but also vinculin and l-afadin, known to bind to ponsin and vinexin. nArgBP2 may be implicated in the protein network around SAPAP in the PSD.

Functional analysis of the guanylate kinase-like domain in the synapse-associated protein SAP97.

Kuhlendahl S, Spangenberg O, Konrad M, Kim E, Garner CC
Eur J Biochem. 1998; 252: 305-13

SAP97 is a membrane cytoskeletal protein localized at the presynaptic nerve terminals of type 1 asymmetric synapses. It has been implicated in the assembly of synapses and in particular in the localization and clustering of ion channels. The C-terminal GK domain of SAP97 shares a high degree of sequence similarity with low-molecular-mass guanylate kinases. These enzymes are involved in the guanine nucleotide metabolic cycle and in the maintenance of GTP/GDP pools required for example in Ras-mediated cell signaling. It has therefore been hypothesized that SAP97 plays an essential role in cellular signaling by regulating the guanine nucleotide pools at synaptic junctions. Here, we test this hypothesis by assessing whether the GK domain in SAP97 encodes an authentic guanylate kinase. We show that the GK domain in and of itself does not encode an active guanylate kinase, that it cannot be activated by its binding partner GKAP and that flanking regions are not acting as inhibitory regulators for enzymatic activity. Thus, it would appear that the GK domain of SAP97 is not involved in the metabolism of guanine nucleotides required for signaling events.

C2-domains, structure and function of a universal Ca2+-binding domain.

Rizo J, Sudhof TC
J Biol Chem. 1998; 273: 15879-82

GKAP, a novel synaptic protein that interacts with the guanylate kinase-like domain of the PSD-95/SAP90 family of channel clustering molecules.

Kim E, Naisbitt S, Hsueh YP, Rao A, Rothschild A, Craig AM, Sheng M
J Cell Biol. 1997; 136: 669-78

The molecular mechanisms underlying the organization of ion channels and signaling molecules at the synaptic junction are largely unknown. Recently, members of the PSD-95/SAP90 family of synaptic MAGUK (membrane-associated guanylate kinase) proteins have been shown to interact, via their NH2-terminal PDZ domains, with certain ion channels (NMDA receptors and K+ channels), thereby promoting the clustering of these proteins. Although the function of the NH2-terminal PDZ domains is relatively well characterized, the function of the Src homology 3 (SH3) domain and the guanylate kinase-like (GK) domain in the COOH-terminal half of PSD-95 has remained obscure. We now report the isolation of a novel synaptic protein, termed GKAP for guanylate kinase-associated protein, that binds directly to the GK domain of the four known members of the mammalian PSD-95 family. GKAP shows a unique domain structure and appears to be a major constituent of the postsynaptic density. GKAP colocalizes and coimmunoprecipitates with PSD-95 in vivo, and coclusters with PSD-95 and K+ channels/NMDA receptors in heterologous cells. Given their apparent lack of guanylate kinase enzymatic activity, the fact that the GK domain can act as a site for protein-protein interaction has implications for the function of diverse GK-containing proteins (such as p55, ZO-1, and LIN-2/CASK).

PDZ domains: targeting signalling molecules to sub-membranous sites.

Ponting CP, Phillips C, Davies KE, Blake DJ
Bioessays. 1997; 19: 469-79

PDZ (also called DHR or GLGF) domains are found in diverse membrane-associated proteins including members of the MAGUK family of guanylate kinase homologues, several protein phosphatases and kinases, neuronal nitric oxide synthase, and several dystrophin-associated proteins, collectively known as syntrophins. Many PDZ domain-containing proteins appear to be localised to highly specialised submembranous sites, suggesting their participation in cellular junction formation, receptor or channel clustering, and intracellular signalling events. PDZ domains of several MAGUKs interact with the C-terminal polypeptides of a subset of NMDA receptor subunits and/or with Shaker-type K+ channels. Other PDZ domains have been shown to bind similar ligands of other transmembrane receptors. Recently, the crystal structures of PDZ domains, with and without ligand, have been determined. These demonstrate the mode of ligand-binding and the structural bases for sequence conservation among diverse PDZ domains.

Tight junctions, membrane-associated guanylate kinases and cell signaling.

Kim SK
Curr Opin Cell Biol. 1995; 7: 641-9

Proteins that define a new family, termed membrane-associated guanylate kinases, have recently been identified as structural components of epithelial tight junctions and neuronal synapses, and as cell signaling proteins in Drosophila and Caenorhabditis elegans. In particular, the lin-2 gene has been shown to encode a membrane-associated guanylate kinase and to act in the let-23 receptor tyrosine kinase/let-60 ras signaling pathway that controls vulval induction in C. elegans. The combined data from recent biochemical and genetic analyses of membrane-associated guanylate kinases suggest that certain tight junction proteins can play an important role in cell signaling pathways. One possibility is that asymmetric segregation of signaling receptors to the basolateral membrane domain of polarized epithelial cells is crucial for proper cell signaling, and that membrane-associated guanylate kinases may be required for this localization.

Three-dimensional structure of the complex of guanylate kinase from yeast with its substrate GMP.

Stehle T, Schulz GE
J Mol Biol. 1990; 211: 249-54

The enzyme guanylate kinase was isolated from baker's yeast and crystallized as a complex with its substrate GMP. The crystal structure was solved by multiple isomorphous replacement, solvent-flattening, restrained least-squares refinement, and simulated annealing. The current R-factor is 28.9% at a resolution of 2.0 A. The model is given as a backbone tracing, the GMP binding site is shown in atomic detail. In its major domain (residues 1 to 32 and 82 to 186), the chain fold is closely similar to the adenylate kinases, while the minor domain (residues 33 to 81) differs grossly from the 3-helix fold of the adenylate kinases. Structural homology and mechanistical similarity allow us to assign the AMP site of the adenylate kinases on the basis of the GMP site.