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Inactive Protein (inactive + protein)
Selected AbstractsUnphosphorylated STAT3 modulates alpha7 nicotinic receptor signaling and cytokine production in sepsisEUROPEAN JOURNAL OF IMMUNOLOGY, Issue 9 2010Geber Peña Abstract The role of STAT3 in infectious diseases remains undetermined, in part because unphosphorylated STAT3 has been considered an inactive protein. Here, we report that unphosphorylated STAT3 contributes to cholinergic anti-inflammation, prevents systemic inflammation, and improves survival in sepsis. Bacterial endotoxin induced STAT3 tyrosine phosphorylation in macrophages. Both alpha7 nicotinic receptor (alpha7nAChR) activation and inhibition of JAK2 blunt STAT3 phosphorylation. Inhibition of STAT3 phosphorylation mimicked the alpha7nAChR signaling, inhibiting NF-,B and cytokine production in macrophages. Transfection of macrophages with the dominant-negative mutant STAT3F, to prevent its tyrosine phosphorylation, reduced TNF production but did not prevent the alpha7nAChR signaling. However, inhibition of STAT3 protein expression enhanced cytokine production and abrogated alpha7nAChR signaling. Alpha7nAChR controls TNF production in macrophages through a mechanism that requires STAT3 protein expression, but not its tyrosine phosphorylation. In vivo, inhibition of STAT3 tyrosine phosphorylation by stattic prevented systemic inflammation and improved survival in experimental sepsis. Stattic also prevented the production of late mediators of sepsis and improved survival in established sepsis. These results reveal the immunological implications of tyrosine-unphosphorylated STAT3 in infectious diseases. [source] Tn5 as a model for understanding DNA transpositionMOLECULAR MICROBIOLOGY, Issue 5 2003William S. Reznikoff Summary Tn5 is an excellent model system for understanding the molecular basis of DNA-mediated transposition. Mechanistic information has come from genetic and biochemical investigations of the transposase and its interactions with the recognition DNA sequences at the ends of the transposon. More recently, molecular structure analyses of catalytically active transposase; transposon DNA complexes have provided us with unprecedented insights into this transposition system. Transposase initiates transposition by forming a dimeric transposase, transposon DNA complex. In the context of this complex, the transposase then catalyses four phosphoryl transfer reactions (DNA nicking, DNA hairpin formation, hairpin resolution and strand transfer into target DNA) resulting in the integration of the transposon into its new DNA site. The studies that elucidated these steps also provided important insights into the integration of retroviral genomes into host DNA and the immune system V(D)J joining process. This review will describe the structures and steps involved in Tn5 transposition and point out a biologically important although surprising characteristic of the wild-type Tn5 transposase. Transposase is a very inactive protein. An inactive transposase protein ensures the survival of the host and thus the survival of Tn5. [source] Chain-length specificities of maize starch synthase I enzyme: studies of glucan affinity and catalytic propertiesTHE PLANT JOURNAL, Issue 5 2001Padmavathi D. Commuri Summary It is widely known that some of the starch synthases and starch-branching enzymes are trapped inside the starch granule matrix during the course of starch deposition in amyloplasts. The objective of this study was to use maize SSI to further our understanding of the protein domains involved in starch granule entrapment and identify the chain-length specificities of the enzyme. Using affinity gel electrophoresis, we measured the dissociation constants of maize SSI and its truncated forms using various glucans. The enzyme has a high degree of specificity in terms of its substrate,enzyme dissociation constant, but has a greatly elevated affinity for increasing chain lengths of ,-1, 4 glucans. Deletion of the N-terminal arm of SSI did not affect the Kd value. Further small deletions of either N- or C-terminal domains resulted in a complete loss of any measurable affinity for its substrate, suggesting that the starch-affinity domain of SSI is not discrete from the catalytic domain. Greater affinity was displayed for the amylopectin fraction of starch as compared to amylose, whereas glycogen revealed the lowest affinity. However, when the outer chain lengths (OCL) of glycogen were extended using the phosphorylase enzyme, we found an increase in affinity for SSI between an average OCL of 7 and 14, and then an apparently exponential increase to an average OCL of 21. On the other hand, the catalytic ability of SSI was reduced several-fold using these glucans with extended chain lengths as substrates, and most of the label from [14C]ADPG was incorporated into shorter chains of dp < 10. We conclude that the rate of catalysis of SSI enzyme decreases with the OCL of its glucan substrate, and it has a very high affinity for the longer glucan chains of dp ,20, rendering the enzyme catalytically incapable at longer chain lengths. Based on the observations in this study, we propose that during amylopectin synthesis shorter A and B1 chains are extended by SSI up to a critical chain length that soon becomes unsuitable for catalysis by SSI and hence cannot be elongated further by this enzyme. Instead, SSI is likely to become entrapped as a relatively inactive protein within the starch granule. Further glucan extension for continuation of amylopectin synthesis must require a handover to other SS enzymes which can extend the glucan chains further or for branching by branching enzymes. If this is correct, this proposal provides a biochemical basis to explain how the specificities of various SS enzymes determine and set the limitations on the length of A, B, C chains in the starch granule. [source] Crystallization of parasporin-2, a Bacillus thuringiensis crystal protein with selective cytocidal activity against human cellsACTA CRYSTALLOGRAPHICA SECTION D, Issue 12-2 2004Toshihiko Akiba Bacillus thuringiensis is a valuable source of protein toxins that are specifically effective against certain insects and worms but harmless to mammals. In contrast, a protein toxin obtained from B. thuringiensis strain A1547, designated parasporin-2, is not insecticidal but has a strong cytocidal activity against human cells with markedly divergent target specificity. The 37,kDa inactive protein is proteolytically activated to a 30,kDa active form. The active form of the recombinant protein toxin was crystallized in the presence of ethylene glycol and polyethylene glycol 8000 at neutral pH. The crystals belong to the hexagonal space group P61 or P65, with unit-cell parameters a = b = 134.37, c = 121.24,Å. Diffraction data from a native crystal were collected to 2.75,Å resolution using a synchrotron-radiation source. [source] GABAA receptor associated proteins: a key factor regulating GABAA receptor functionJOURNAL OF NEUROCHEMISTRY, Issue 2 2007Zi-Wei Chen Abstract ,-Aminobutyric acid (GABA), an important inhibitory neurotransmitter in both vertebrates and invertebrates, acts on GABA receptors that are ubiquitously expressed in the CNS. GABAA receptors also represent a major site of action of clinically relevant drugs, such as benzodiazepines, barbiturates, ethanol, and general anesthetics. It has been shown that the intracellular M3-M4 loop of GABAA receptors plays an important role in regulating GABAA receptor function. Therefore, studies of the function of receptor intracellular loop associated proteins become important for understanding mechanisms of regulating receptor activity. Recently, several labs have used the yeast two-hybrid assay to identify proteins interacting with GABAA receptors, for example, the interaction of GABAA receptor associated protein (GABARAP) and Golgi-specific DHHC zinc finger protein (GODZ) with , subunits, PRIP, phospholipase C-related, catalytically inactive proteins (PRIP-1) and (PRIP-2) with GABARAP and receptor ,2 and , subunits, Plic-1 with some , and , subunits, radixin with the ,5 subunit, HAP1 with the ,1 subunit, GABAA receptor interacting factor-1 (GRIF-1) with the ,2 subunit, and brefeldin A-inhibited GDP/GTP exchange factor 2 (BIG2) with the ,3 subunit. These proteins have been shown to play important roles in modulating the activities of GABAA receptors ranging from enhancing trafficking, to stabilizing surface and internalized receptors, to regulating modification of GABAA receptors. This article reviews the current studies of GABAA receptor intracellular loop-associated proteins. [source] | ||||||||||