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91.
Arun Kannan Weishan Huang Fei Huang Avery August 《The international journal of biochemistry & cell biology》2012,44(12):2129-2134
T cells play an indispensable role in immune defense against infectious agents, but can also be pathogenic. These T cells develop in the thymus, are exported into the periphery as naïve cells and participate in immune responses. Upon recognition of antigen, they are activated and differentiate into effector and memory T cells. While effector T cells carry out the function of the immune response, memory T cells can last up to the life time of the individual, and are activated by subsequent antigenic exposure. Throughout this life cycle, the T cell uses the same receptor for antigen, the T cell Receptor, a complex multi-subunit receptor. Recognition of antigen presented by peptide/MHC complexes on antigen presenting cells unleashes signaling pathways that control T cell activation at each stage. In this review, we discuss the signals regulated by the T cell receptor in naïve and effector/memory T cells. 相似文献
92.
The precise positioning of the flexible C-helix in the catalytic core is a critical step in the activation of most protein kinases. Consequently, the alphaC-beta4 loop, which anchors the C-helix to the catalytic core, is highly conserved and mediates key structural interactions that serve as a hinge for C-helix movement. While these hinge interactions are conserved across diverse eukaryotic protein kinase structures, some families such as AGC kinases diverge from the canonical hinge interactions. This divergence was recently proposed to facilitate an alternative mode of regulation wherein a conserved C-terminal tail interacts with the alphaC-beta4 loop to position the C-helix. Here we show how interactions between the alphaC-beta4 loop and the N-terminal SH2 domain of ZAP-70 tyrosine kinase are mechanistically and functionally analogous to interactions between the alphaC-beta4 loop and the C-terminal tail of AGC kinases. Such cis regulation of protein kinase activity may be a feature of other eukaryotic protein kinase families as well. 相似文献
93.
Thanukrishnan Kannan Duraikkannu Loganathan Yukti Bhatia Saroj Mishra Virendra S. Bisaria 《Biocatalysis and Biotransformation》2004,22(1):1-7
The stability of almond β-glucosidase in five different organic media was evaluated. After 1 hour of incubation at 30°C, the enzyme retained 95, 91, 81, 74 and 56% relative activity in aqueous solutions [30% (v/v)] of dioxane, DMSO, DMF, acetone and acetonitrile, respectively. Transglucosylation involving p-nitrophenyl β-D-glucopyranoside as donor and β-1-N-acetamido-D-glucopyranose, which is a glycosylasparagine mimic, as acceptor was explored under different reaction conditions using almond βglucosidase and cloned Pichia etchellsii β-glucosidase II. The yield of disaccharides obtained in both reactions turned out to be 3%. Both enzymes catalyzed the formation of (1→3)- as well as (1→6)- regioisomeric disaccharides, the former being the major product in cloned β-glucosidase II reaction while the latter predominated in the almond enzyme catalyzed reaction. Use of β-1-N-acetamido-D-mannopyranose and β-1-N-acetamido-2-acetamido-2-deoxy-D-glucopyranose as acceptors in almond β-glucosidase catalyzed reactions, however, did not afford any disaccharide products revealing the high acceptor specificity of this enzyme. 相似文献
94.
Active Subtilisin-Like Protease from a Hyperthermophilic Archaeon in a Form with a Putative Prosequence 总被引:6,自引:2,他引:4 下载免费PDF全文
Yuji Kannan Yuichi Koga Yohei Inoue Mitsuru Haruki Masahiro Takagi Tadayuki Imanaka Masaaki Morikawa Shigenori Kanaya 《Applied microbiology》2001,67(6):2445-2452
The gene encoding subtilisin-like protease T. kodakaraensis subtilisin was cloned from a hyperthermophilic archaeon Thermococcus kodakaraensis KOD1. T. kodakaraensis subtilisin is a member of the subtilisin family and composed of 422 amino acid residues with a molecular weight of 43,783. It consists of a putative presequence, prosequence, and catalytic domain. Like bacterial subtilisins, T. kodakaraensis subtilisin was overproduced in Escherichia coli in a form with a putative prosequence in inclusion bodies, solubilized in the presence of 8 M urea, and refolded and converted to an active molecule. However, unlike bacterial subtilisins, in which the prosequence was removed from the catalytic domain by autoprocessing upon refolding, T. kodakaraensis subtilisin was refolded in a form with a putative prosequence. This refolded protein of recombinant T. kodakaraensis subtilisin which is composed of 398 amino acid residues (Gly−82 to Gly316), was purified to give a single band on a sodium dodecyl sulfate (SDS)-polyacrylamide gel and characterized for biochemical and enzymatic properties. The good agreement of the molecular weights estimated by SDS-polyacrylamide gel electrophoresis (44,000) and gel filtration (40,000) suggests that T. kodakaraensis subtilisin exists in a monomeric form. T. kodakaraensis subtilisin hydrolyzed the synthetic substrate N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide only in the presence of the Ca2+ ion with an optimal pH and temperature of pH 9.5 and 80°C. Like bacterial subtilisins, it showed a broad substrate specificity, with a preference for aromatic or large nonpolar P1 substrate residues. However, it was much more stable than bacterial subtilisins against heat inactivation and lost activity with half-lives of >60 min at 80°C, 20 min at 90°C, and 7 min at 100°C. 相似文献
95.
96.
97.
Swaminathan Palanisami Krishna Kannan Uma Lakshmanan 《Journal of applied phycology》2012,24(5):1093-1098
The marine cyanobacterium Phormidium valderianum BDU 140441 exhibited the ability to grow at 0.25?mM tannic acid, a known hindering chemical for microbial growth. The tannic acid-degrading ability of the organism is evident from the UV–visible absorption spectrum. In addition, the existence of tannase has been localized by activity staining, and its induction in activity upon tannic acid exposure was confirmed in native gel. The critical tannic acid metabolization enzymes tested for are polyphenol oxidase and esterases; both are well known for tannic acid degradation. Upon tannic acid exposure, increased activity of polyphenol oxidase and expression of few new isoforms of esterase were identified by activity staining. 相似文献
98.
Paliakkara L. Jaison Vadakkedath M. Kannan Mandagini Geetha Padinjaradath S. Appukuttan 《Journal of biosciences》1993,18(2):187-193
Naturally occurring serum IgG against terminal α-galactoside epitopes (anti-Gal), present exclusively in man, apes and old
world monkeys, was used as probe for these epitopes in human brain. Human brain grey matter soluble glycoproteins enriched
inα galactosyl groups by affinity chromatography on jacalin-sepharose, specifically binds to human anti-Gal in immuno dot
blots. Anti-Gal recognized exclusively the terminal α galactoside epitope in human brain glycoproteins since binding was abolished
by the presence of 1-0-methyl α-D-galactopyranoside as well as by pretreatment of glycoproteins with coffee bean α-galactosidase.
Anti-Gal-peroxidase staining of jacalin-binding human brain glycoproteins in western immuno blots revealed mainly five anti-Gal-binding
polypeptides withM
r
(in kDa) of 94, 108, 180, 210 and 230 respectively. Since the presence of anti-Gal in higher animals accompanies suppression
of the corresponding epitope in most tissues, apparently to maintain immunological balance, possible implications of the above
observation for autoimmunity, tumor metastasis and infection are discussed. 相似文献
99.
Zac Yates Kannan Gunasekaran Hongxing Zhou Zhonghua Hu Zhi Liu Randal R. Ketchem Boxu Yan 《The Journal of biological chemistry》2010,285(24):18662-18671
Hydroxyl radicals induce hinge cleavage in a human IgG1 molecule via initial radical formation at the first hinge Cys231 followed by electron transfer to the upper hinge residues. To enable engineering of a stable monoclonal antibody hinge, we investigated the role of the hinge His229 residue using structure modeling and site-directed mutagenesis. Direct involvement of His229 in the reaction mechanism is suggested by a 75–85% reduction of the hinge cleavage for variants in which His229 was substituted with either Gln, Ser, or Ala. In contrast, mutation of Lys227 to Gln, Ser, or Ala increased hinge cleavage. However, the H229S/K227S double mutant shows hinge cleavage levels similar to that of the single H229S variant, further revealing the importance of His229. Examination of the hinge structure shows that His229 is capable of forming hydrogen bonds with surrounding residues. These observations led us to hypothesize that the imidazole ring of His229 may function to facilitate the cleavage by forming a transient radical center that is capable of extracting a proton from neighboring residues. The work presented here suggests the feasibility of engineering a new generation of monoclonal antibodies capable of resisting hinge cleavage to improve product stability and efficacy. 相似文献
100.
Nayoung Kang Ah Hyun Jun Yangzom Doma Bhutia Natarajan Kannan Jashvant D. Unadkat Rajgopal Govindarajan 《The Journal of biological chemistry》2010,285(36):28343-28352
Accumulating evidence reveals that sole mutations in hENT3 cause a spectrum of human genetic disorders. Among these include H syndrome, characterized by scleroderma, hyperpigmentation, hypertrichosis, hepatomegaly, cardiac abnormalities and musculoskeletal deformities, pigmented hypertrichotic dermatosis with insulin-dependent diabetes syndrome, characterized by autoantibody-negative diabetes mellitus and skin deformities, familial Rosai-Dorfman disease, characterized by short stature, familial histiocytosis and sinus histiocytosis with massive lymphadenopathy (SHML), characterized by severe tissue infiltration of immune cells and swollen lymph nodes. hENT3 spectrum disorders share a common mutation and share overlapping clinical manifestations that display many intriguing resemblances to mitochondrial and lysosomal disorders. Although earlier studies identify hENT3 as a mitochondrial and a lysosomal nucleoside transporter, the precise connections between hENT3 and the pathophysiology of these disorders remain unresolved. In this study, we performed functional and biochemical characterization of these mutations in hENT3. We report severe reductions/losses of hENT3 nucleoside transport functions of hENT3 syndrome mutants. In addition to transport alterations, we provide evidence for possible loss of hENT3 functions in all H and pigmented hypertrichotic dermatosis with insulin-dependent diabetes syndromes due to either mistrafficking or altered stability of mutant hENT3 proteins. 相似文献