Poly-gamma-glutamic acid (gamma-PGA) is a very promising biodegradable polymer that is produced by Bacillus subtilis. Gamma-PGA is water-soluble, anionic, biodegradable, and edible. This paper reviews the production of a strain of gamma-PGA and recent developments with respect to applications in terms of Ca absorption, moisturizing properties, gamma-PGA conjugation, super absorbent polymer, and so on. Our recent research shows that gamma-PGA can be used as an immune-stimulating and anti-tumor agent, especially at high molecular weight.

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The Class I and III polyhydroxybutyrate (PHB) synthases from Ralstonia eutropha and Chromatium vinosum, respectively, catalyze the polymerization of beta-hydroxybutyryl-coenzyme A (HBCoA) to generate PHB. These synthases have different molecular weights, subunit composition, and kinetic properties. Recent studies with the C. vinosum synthase suggested that it is structurally homologous to bacterial lipases and allowed identification of active site residues important for catalysis [Jia, Y., Kappock, T. J., Frick, T., Sinskey, A. J., and Stubbe, J. (2000) Biochemistry 39, 3927-3936]. Sequence alignments between the Class I and III synthases revealed similar residues in the R. eutropha synthase. Site-directed mutants of these residues were prepared and examined using HBCoA and a terminally saturated trimer of HBCoA (sT-CoA) as probes. These studies reveal that the R. eutropha synthase possesses an essential catalytic dyad (C319-H508) in which the C319 is involved in covalent catalysis. A conserved Asp, D480, was shown not to be required for acylation of C319 by sT-CoA and is proposed to function as a general base catalyst to activate the hydroxyl of HBCoA for ester formation. Studies of the [(3)H]sT-CoA with wild-type and mutant synthases reveal that 0.5 equiv of radiolabel is covalently bound per monomer of synthase, suggesting that a dimeric form of the enzyme is involved in elongation. These studies, in conjunction with search algorithms for secondary structure, suggest that the Class I and III synthases are mechanistically similar and structurally homologous, despite their physical and kinetic differences.

Sphingosine-1 Phosphate (S1P) helps mediate lymphocyte egress from lymph nodes, yet significant mechanistic questions remain. Here we show that B lymphocyte egress sites exist close to lymph node follicles. Recent B cell emigrants localize towards follicle centers, while longer-term residents tend towards cortical sinusoids. Exiting B lymphocytes squeeze through apparent portals in the lymphatic endothelium. Treatment with the S1P receptor agonist FTY720 empties the cortical sinusoids of lymphocytes, blocks lymphatic endothelial penetration, and displaces B lymphocytes into the T cell zone. S1P3−/− B cells, which lack chemoattractant responses to S1P, transit lymph nodes normally, while Gnai2−/− B cells, which have impaired responses to chemokines and S1P, transit more rapidly than do wild type cells. This study identifies a major site of B lymphocyte lymph node egress, shows that FTY720 treatment blocks passage through the cortical lymphatic endothelium, and argues against a functional role for S1P chemotaxis in B lymphocyte egress.

ERM (ezrin, radixin moesin) proteins in lymphocytes link cortical actin to plasma membrane, which is regulated in part by ERM protein phosphorylation. To assess whether phosphorylation of ERM proteins regulates lymphocyte migration and membrane tension, we generated transgenic mice whose T-lymphocytes express low levels of ezrin phosphomimetic protein (T567E). In these mice, T-cell number in lymph nodes was reduced by 27%. Lymphocyte migration rate in vitro and in vivo in lymph nodes decreased by 18% to 47%. Lymphocyte membrane tension increased by 71%. Investigations of other possible underlying mechanisms revealed impaired chemokine-induced shape change/lamellipod extension and increased integrin-mediated adhesion. Notably, lymphocyte homing to lymph nodes was decreased by 30%. Unlike most described homing defects, there was not impaired rolling or sticking to lymph node vascular endothelium but rather decreased migration across that endothelium. Moreover, decreased numbers of transgenic T cells in efferent lymph suggested defective egress. These studies confirm the critical role of ERM dephosphorylation in regulating lymphocyte migration and transmigration. Of particular note, they identify phospho-ERM as the first described regulator of lymphocyte membrane tension, whose increase probably contributes to the multiple defects observed in the ezrin T567E transgenic mice. (Blood. 2012;119(2):445-453) IntroductionNormal immune function depends on lymphocytes in circulation binding to vascular endothelium, transmigrating across the endothelium, and migrating within tissue. 1-3 Lymphocyte migration and transmigration depend on cytoskeletal reorganization, including especially the actin cytoskeleton. However, linkage between plasma membrane and actin cytoskeleton is a potentially important aspect, which has not yet been well studied. Ezrin-radixin-moesin (ERM) proteins are a trio of very closely related human paralogs whose primary function is mediating linkage between the plasma membrane and cortical actin, which is the shell of polymerized actin that lies just below the membrane. 4,5 One of the most fundamental aspects of ERM protein function is their ability to regulate that linkage by switching between active and inactive conformations. In the active conformation, the N-terminal region, the FERM domain, binds to plasma membrane lipids and cytoplasmic tails of transmembrane proteins and the C-terminal region binds to F-actin. However, in the dormant conformation, those 2 regions bind intramolecularly to each other and therefore cannot mediate linkage via intermolecular interactions. The conformational switch between dormant and active forms is initiated and sustained by ERM protein binding to PI(4,5)P2 in the plasma membrane. [4][5][6][7] In addition, C-terminal phosphorylation plays an important role in stabilizing the active conformation. Solved structures of the dormant ERM protein elucidate the mechanism whereby phosphorylation stabilizes the active conformation. The critical threonine that is phosphorylated ...

Interleukin-7 (IL-7 IntroductionInterleukin-7 (IL-7) is a nonredundant cytokine that plays an essential role in lymphopoiesis and in the homeostasis of the T-lymphoid compartment in adults. 1,2 IL-7 is produced at constitutive levels by stromal cells resident in various organs, as well as by thymic and intestinal epithelial cells. 3 Under physiologic conditions, IL-7 supports long-term survival of naive and memory T cells without inducing proliferation, thereby maintaining the regular size of the T-cell pool. 2 Under conditions of lymphopenia, the concentration of IL-7 rises to suprahomeostatic levels (as reflected by plasma concentrations greater than 10 pg/mL) that induce proliferation of both naive and memory T cells with the aim of reconstituting the physiologic T-cell pool, a process commonly referred to as lymphopenia-induced proliferation. 2 Because of these unique biologic properties and lack of side effects typically associated with other cytokines such as IL-2, IL-7 is currently under clinical evaluation as an immune-reconstitution agent in various forms of immunodeficiencies, including those associated with AIDS and cancer. 4 Short-term courses of IL-7 administration in humans and macaques were shown to result in proliferation of both CD4 ϩ and CD8 ϩ T cells, with preferential expansion of naive T cells associated with increased diversification of the T-cell receptor (TCR) repertoire. [5][6][7][8][9] Remarkably, injection of IL-7 induces a rapid, albeit transient, reduction in circulating lymphocyte counts compatible with redistribution of these cells to peripheral tissues. 6,7 This phenomenon may reflect events that occur naturally when endogenous IL-7 increases to suprahomeostatic levels in response to lymphopenia. Although data obtained in macaques have suggested that lymph nodes, parts of the intestine, and the skin may be homing sites for T cells after IL-7 injection, 10 the anatomical sites where homeostatic processes take place and the molecular mechanisms underlying the IL-7-driven homing and proliferation of T cells in peripheral tissues remain largely undefined.The circulation of T cells from blood to secondary lymphoid organs and other tissues is governed by a complex network of tissue-homing mechanisms, which mainly relies on integrins, chemokine receptors, and their specific ligands. 11 In this study, we show that IL-7 selectively induces expression and functional activation of integrin ␣4␤7, the main intestinal lymphocyte homing receptor, [11][12][13][14] both in vitro and in vivo. This effect occurs predominantly in naive T cells, which indeed showed a marked and selective in vivo homing to the intestinal compartment of humanized mice after treatment with IL-7. The evidence presented in this study provides a mechanism for the rapid reduction of circulating T cells after in vivo IL-7 administration and suggests that ␣4␤7-mediated gut homing of naive T cells may be a fundamental step in the IL-7-driven T-cell reconstitution of lymphopenic hosts. Methods Cells and culture conditionsPeriphe...

The intestinal mucosa is a key anatomical site for HIV-1 replication and CD4+ T-cell depletion. Accordingly, in vivo treatment with an antibody to the gut-homing integrin α4β7 was shown to reduce viral transmission, delay disease progression, and induce persistent virus control in macaques challenged with SIV. Here, we show that integrin α4β7 is efficiently incorporated into the envelope of HIV-1 virions. Incorporated α4β7 is functionally active as it binds MAdCAM-1, promoting HIV-1 capture by and infection of MAdCAM-expressing cells, which in turn mediate trans-infection of bystander cells. Functional α4β7 is present in circulating virions from HIV-infected patients and SIV-infected macaques, with peak levels during the early stages of infection. In vivo homing experiments documented selective and specific uptake of α4β7+ HIV-1 virions by high endothelial venules in the intestinal mucosa. These results extend the paradigm of tissue homing to a retrovirus and are relevant for the pathogenesis, treatment and prevention of HIV-1 infection.