PTyr Surrogates as PTP Inhibitors

X-ray crystallographic studies have revealed a very similar active site (the pTyr binding site) for PTPs. In the substrate-bound form of PTP1B, the terminal non-bridge phosphate oxygens of pTyr form an extensive array of hydrogen bonds with the main-chain nitrogens of the PTP signature motif (residues 215-221) and the guanidinium side chain of Arg221. The phenyl ring of the pTyr is engaged in hydrophobic interactions with the active-site cavity, formed by the nonpolar side chains of Val49,...

The Role of GSK3 in Embryonic Development

It is well established that GSK3 plays a key role in embryonic development as a central player in the Wnt signaling pathway. In this pathway, GSK3 is present in a complex that contains at least three other proteins Axin, P-catenin, and the adenomatous polyposis coli (APC) protein 33 . Axin acts as a scaffold by binding to GSK3, P-catenin, and APC, while APC also interacts with P-catenin. In this complex, GSK3 is active and phosphorylates Axin, P-catenin and APC. The phosphorylation of Axin...

Implications of the vIL6gp130 Tetramer Structure for the Active Gcsfgcsfr Extracellular Signaling Complex

A crystal structure has been reported for GCSF in complex with the CHR (domains 2 and 3 also called the BN and BC domains, respectively) of the GCSFR (Fig. 2A) 2 . The structure revealed both expected and unexpected results. The complex is a 2 2 tetramer, with each GCSF molecule interacting with each receptor through the canonical site 2 epitope (also called major interface) on the face of the A and C helices (Fig. 2A) 2 . However, the unexpected result was that the two GCSF GCSFR complexes...

The Future Ion Channels as Electrosomes

Beyond the classical pore-forming subunits and auxillary subunits that comprise ion channels, it is becoming ever more clear that, in real biological settings, ion channels are part of large protein networks. These networks include cytoskeletal components, signaling proteins such as protein kinases and phosphatases, and channel-associated proteins that recruit these signaling molecules to the channel to modify its function. To understand the biological structure of ion channels, it will be...

Stress Responsive PP2Cs in Bacillus subtilis

Bacillus subtilis has five PP2C-like phosphatases, SpoIIE, PrpC, RsbU, RsbX, and RsbP, with the latter three involved in the regulation of the general stress-responsive oB factor. The oB transcription factor can be activated by energy stress (i.e., starvation of carbon, phosphate, or oxygen) or environmental stress (i.e., high salt, heat shock, or ethanol), leading to the induction of many stress-response genes 27 . Energy and environmental stresses are transmitted by distinct signaling...

INAD Organizes Signaling Complexes

Phototransduction in Drosophila is one of the fastest G-protein-coupled signaling pathways known, taking less than 20 ms from light activation to maximum response. This high speed of signaling is primarily due to the incorporation of signaling components into multi-protein complexes. Signaling complexes bring components into close proximity, promoting rapid interaction as well as ensuring the proper sub-cellular localization of components. The central organizer of these signaling complexes is...

Budding Yeast Cdc14 is Essential for Exit from Mitosis

Following their association with B-type cyclins, the activation of cyclin-dependent kinases (Cdk) triggers the onset of mitosis. At anaphase after sister chromatids have separated, mitotic Cdks must be inactivated in order for cells to exit from mitosis. During exit from mitosis, cells restore the nucleus to its premitotic state (e.g., disassemble the mitotic spindle) and prepare for cytokinesis (for review, see Morgan 5 ). A prevailing mechanism for mitotic Cdk inactivation is the regulated...

The Redundant Chemokine System Is an Optimal Target for Viral Exploitation

Chemokines are chemotactic cytokines, which primarily control the migration but also the activation and differentiation of all subsets of leukocytes and play important roles in angio-genesis, organogenesis, and carcinogenesis 1 . Chemokines act through a large family of G-protein-coupled receptors, which are divided into subfamilies of CXC, CC, and CX3C receptors. This nomenclature refers to a fingerprint sequence in the ligands where the first two Cys residues are either neighbors (CC) or...

Functional Consequences of GPCR Endocytosis

Role in Rapid Desensitization of GPCRs In many cases, endocytosis is not thought to play a primary role in mediating rapid desensitization of many GPCRs, although the precise role of endocytosis in this process may depend on receptor expression level. Endocytosis of -opioid receptors does not contribute significantly to functional desen-sitization in cells expressing relatively high levels of receptor protein but does appear to cause desensitization in cells expressing lower levels of receptor...

Mark L Mayer

Laboratory of Cellular and Molecular Neurophysiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland At the majority of excitatory synapses in the brain, the amino acid l-glutamate acts as the neurotransmitter that is released by calcium-dependent exocytosis from presynaptic nerve terminals. After diffusion across the synaptic cleft, molecules of l-glutamate bind to two families of neurotransmitter receptors in the postsynaptic...

The Voltage Sensing Gating Particle

Before the advent of molecular biology, through classical electrophysiology experiments, Hodgkin and Huxley 14 established the physical basis for action potential generation and propagation. Working in squid giant axon, they demonstrated that the action potential consists of two voltage-dependent currents carried by an initial inward Na+ flux followed by an outward K+ flux. Hodgkin and Huxley hypothesized that voltage controlled the Na+ and K+ conductances by biasing the equilibrium of charged...

Oxidation of PTPs in Tyrosine Phosphorylation Dependent Signaling

Reactive oxygen species (ROS) are produced in response to a wide variety of cellular stimuli 52 . A substantial body of data emphasizes the importance of ROS production as a mechanism for fine-tuning tyrosine-phosphorylation-dependent signaling through the transient oxidation and inactivation of members of the PTP family 53 . In the unique environment of the PTP active site, the invariant Cys residue of the signature motif, which displays an unusually low pKa, is present predominantly as the...

Medical Implications of the AMPK System

Type 2 diabetes, which affects over 100 million people worldwide, is a hyperglycemic condition caused by reduced glucose uptake by muscle and increased glucose production by liver. Physical exercise is known to provide protection against its development, and because AMPK is activated by exercise it regulates the activity and expression of the insulin-sensitive glucose transporter GLUT4 and inhibits expression of enzymes of gluconeogenesis 30 , this suggesting that AMPK could be a promising...

Bidentate PTP Inhibitors

Although pTyr is essential for peptide protein substrate recognition, pTyr alone does not possess high affinity for PTPs 45 . This and the fact that the PTP active site (pTyr binding site) is highly conserved among various PTPs present a serious challenge for the development of potent and selective PTP inhibitors targeted primarily to the active site. The discovery of a second aryl phosphate-binding site in PTP1B (defined by residues Arg24, Arg254, Met258, Gly259, and Gln262), which is not...

Abraham M de Vos and 2Christian Wiesmann

Department of Protein Engineering, Genentech, Inc., South San Francisco, California 2Sunesis-Pharmaceuticals, Inc., South San Francisco, California Nerve growth factor (NGF) is the founding member of the neurotrophins, a family of growth factors responsible for the formation and maintenance (survival or apoptosis) of neuronal populations in the peripheral and central nervous system. The neurotrophins are of potential therapeutic interest in a number of neurological disorders such as Alzheimer's...

FGFR Tyrosine Kinases

FGFs elicit activity through activation of transmembrane FGF receptor tyrosine kinases in partnership with HS pro-teoglycans. The FGFR monomer is composed of a single polypeptide chain that has a glycosylated extracellular ligand-binding domain, a transmembrane domain flanked by jux-tamembrane sequences, and an intracellular tyrosine kinase followed by a C-terminal domain (Fig. 1). The intracellular juxtamembrane region may be a determinant of conforma-tional activation and interaction of the...

PP2A and Wnt Signaling

During embryogenesis, the Wnt signaling pathway regulates cell proliferation and development 26 . An inappropriate activation of the Wnt pathway has been found in a wide variety of human cancers 24 , where it promotes the growth of cancer cells by inducing cyclin D and c-myc. Currently, three genetic changes that cause an increase in p-catenin levels and activation of the Wnt signaling pathway are known. First, some mutations in the p-catenin gene alter specific N-terminal serine or threonine...

S4 Is the Primary Voltage Sensor

A high-resolution structure of the voltage-sensing domain of an ion channel has yet to be obtained however, some things are already known about the structure of this domain. S1 to S6 form transmembrane helices 8,13,14,19,25,33 . The S4 helix is conserved across voltage-gated cation channels and contains a positively charged arginine (R) or lysine (K) at every third position (Fig. 4). Because S4 spans the membrane, some of these charges sense the electric field. The spacing of positive charges...

Interaction Domains A Common Theme in Signaling

Interaction domains are essential in signaling from many different types of cell-surface receptors, as well as in cellular events such as the cell cycle, protein and vesicle trafficking, targeted protein degradation, DNA repair, and control of the cytoskeleton. Thus, the SH2 domain serves as a prototype for a growing family of protein-interaction modules (Table 1), some of which specifically recognize posttranslationally modified motifs, in a fashion akin to the selective binding of SH2 and PTB...

IRSProteins and Insulin Signaling

Insulin and IGF1 receptors, like the receptors for other growth factors and cytokines, are composed of an extracellular ligand-binding domain that controls the conformation and activity of the intracellular tyrosine kinase 9,10 . Unlike most receptor tyrosine kinases that are activated upon ligand-induced dimerization, insulin and IGF1 receptors exist as inactive covalent dimers composed of two extracellular a-subunits and two transmembrane P-subunits. Insulin and IGF1 bind between the two...

Insulin Receptor Domain Structure

The insulin receptor (IR) is a glycosylated, disulfide-linked homodimer, with each monomer being made up of an a-chain that is entirely extracellular and a P-chain that spans the cell membrane once. The a-chain contains the insulin-binding determinants of the receptor, while the intracellular portion of the P-chain includes a protein-tyrosine kinase domain and domains involved in binding signal transduction proteins. The aP monomer of the IR is encoded by a gene with 22 exons alternative...

Comparative Kinomics

A great deal can be learned about the evolution of the protein kinase superfamily through the comparison of the kinomes of different eukaryotes 7,8 (Figures 1 and 2). Fifty one protein kinase families are common to all eukary-otes these serve cell essential functions examples are Cdk, CAMK, PKA, MAP kinase, etc. Interestingly, most of the atypical protein kinase families exist in all four kinomes yeasts, but clearly were not selected for diversification during evolution. Seven families are...

BMP2BRIAec Complex

Figure 1 Superposition (stereo) of the receptor chains mActR-IIec (blue), BR-IAec (red), and TGFPR-IIec (green). The view is looking down onto the central part of the common ligand binding epitopes of BR-IAec and ActR-IIec (the palm of the receptor hand, shaded magenta). The region shaded in red marks marks the position of the highly conserved hydropho-bic residue of type I receptors (Phe85 in BR-IA) that fits into a conserved hydrophobic pocket of the ligand. The ligand binding area of...

Recognition in the Context of a Humoral Immune Response

An understanding of the parameters governing the HIV-1 receptor interactions would be incomplete without an understanding of the context in which this recognition occurs. While all recognitions pit specific versus non-specific interactions, HIV-1 receptor recognition occurs in the context of a persistent infection. In order to bind to receptor while simultaneously eluding neutralization by the humoral immune system, gp120 has evolved sophisticated strategies of evasion (Fig. 3) 17,22,27 . Three...

Serthr Kinase Inhibitors

Among the few hundred Ser Thr kinases a handful are involved in transmitting the signals of upstream PTKs, and their activity is essential for cell proliferation and the onset of anti-apoptotic signaling (Fig. 7). Their abnormal enhanced activities are augmented by the deletion of negative regulators such as protein inhibitors of Cdks and the deletion of the tumor suppressor PTEN, the negative regulator of the PI3' kinase pathway. Thus, the activities of these kinases are enhanced by the...

Subcellular Localization of ErbB Proteins

The localization of LET-23 at the basolateral face of precursor epithelial cells is important for vulval development in C. elegans. In mammalian skeletal muscle, the clustering of ErbB2, ErbB3, and ErbB4 at the postsynaptic membrane of neuromuscular junctions is required for efficient binding to neuron-derived neuregulins and subsequent induction of acetylcholine receptor synthesis. In polarized epithelial cells, most EGFR and ErbB2 molecules are localized to the basolateral face where...

The Regulation of GSK3 Activity by Insulin and Growth Factors

GSK3 can be inhibited via the phosphorylation of a serine residue near the N terminus of the protein (Ser21 in GSK3a, Ser9 in GSK3P) 22 . This serine lies in an Arg-Xaa-Arg-Xaa-Xaa-Ser sequence, which is a consensus motif for phosphorylation by several protein kinases that are components of different signal transduction pathways (Fig. 1). Protein kinase B (PKB, also called Akt) inhibits GSK3 in response to signals that activate class I phos-phatidylinositol (PtdIns) 3-kinases and elevate the...

Protein Tyrosine Kinase Inhibitors

Although protein kinases have been known since the discovery of protein phosphorylation in the 1950s, no one turned to them as drug targets until protein kinase C (PKC) and tyrosine phosphorylation were discovered over 20 years later. Identifying tyrosine kinase activity as being the hallmark of the oncogenic activity of pp60c-Src (and dozens of other oncoproteins) prompted researchers to investigate these proteins as novel targets for drugs. Tyrosine phosphorylation inhibitors (tyrphostins)...

Phenotype of PDK1 PKB and S6KDeficient Mice and Model Organisms

PDK1- - mouse embryos die at day E9.5, displaying multiple abnormalities that include a lack of somites, forebrain, and neural-crest-derived tissues, although the development of the hind- and midbrain proceeds relatively normally 68 . Other eukaryotic organisms also possess homologs of PDK1 that activate homologs of PKB and S6K in these species 69 . As in mice, knocking out PDK1 homologs in yeast 70-72 , Caenorhabditis elegans 73 , and Drosophila 74,75 results in nonviable organisms, confirming...