The generation of influenza-specific humoral responses is impaired in ST6Gal I-deficient mice.

Posttranslational modification of proteins, such as glycosylation, can impact cell signaling and function. ST6Gal I, a glycosyltransferase expressed by B cells, catalyzes the addition of alpha-2,6 sialic acid to galactose, a modification found on N-linked glycoproteins such as CD22, a negative regulator of B cell activation. We show that SNA lectin, which binds alpha-2,6 sialic acid linked to galactose, shows high binding on plasma blasts and germinal center B cells following viral infection, suggesting ST6Gal I expression remains high on activated B cells in vivo. To understand the relevance of this modification on the antiviral B cell immune response, we infected ST6Gal I(-/-) mice with influenza A/HKx31. We demonstrate that the loss of ST6Gal I expression results in similar influenza infectivity in the lung, but significantly reduced early influenza-specific IgM and IgG levels in the serum, as well as significantly reduced numbers of early viral-specific Ab-secreting cells. At later memory time points, ST6Gal I(-/-) mice show comparable numbers of IgG influenza-specific memory B cells and long-lived plasma cells, with similarly high antiviral IgG titers, with the exception of IgG2c. Finally, we adoptively transfer purified B cells from wild-type or ST6Gal I(-/-) mice into B cell-deficient (microMT(-/-)) mice. Recipient mice that received ST6Gal I(-/-) B cells demonstrated reduced influenza-specific IgM levels, but similar levels of influenza-specific IgG, compared with mice that received wild-type B cells. These data suggest that a B cell intrinsic defect partially contributes to the impaired antiviral humoral response.

Neuronal Ca2+ signaling via caldendrin and calneurons.

The calcium sensor protein caldendrin is abundantly expressed in neurons and is thought to play an important role in different aspects of synapto-dendritic Ca2+ signaling. Caldendrin is highly abundant in the postsynaptic density of a subset of excitatory synapses in brain and its distinct localization raises several decisive questions about its function. Previous work suggests that caldendrin is tightly associated with Ca2+ - and Ca2+ release channels and might be involved in different aspects of the organization of the postsynaptic scaffold as well as with synapse-to-nucleus communication. In this report we introduce two new EF-hand calcium sensor proteins termed calneurons that apart from calmodulin represent the closest homologues of caldendrin in brain. Calneurons have a different EF-hand organization than other calcium sensor proteins, are prominently expressed in neurons and will presumably bind Ca2+ with higher affinity than caldendrin. Despite some significant structural differences it is conceivable that they are involved in similar Ca2+ regulated processes like caldendrin and neuronal calcium sensor proteins.

Crystallization and preliminary X-ray crystallographic investigations on a betagamma-crystallin domain of absent in melanoma 1 (AIM1), a protein from Homo sapiens.

AIM1g1 is a single betagamma-crystallin domain from the protein absent in melanoma 1 (AIM1), which appears to play a role in the suppression of melanomas. This domain is known to bind calcium and its structure would help in identifying calcium-coordinating sites in vertebrate crystallins, which have hitherto been believed to have lost this ability during evolution. Crystallization of this domain was performed by the hanging-drop vapour-diffusion method. Crystals diffracted to a maximum resolution of 1.86 A and were found to belong to space group P6(1) or P6(5), with unit-cell parameters a = b = 54.98, c = 59.73 A. Solvent-content analysis indicated the presence of one monomer per asymmetric unit.

Both systemic and mucosal LCMV immunization generate robust viral-specific IgG in mucosal secretions, but elicit poor LCMV-specific IgA.

Immunoglobulins in secretions play a critical role in protection at mucosal surfaces. We examined the generation of viral-specific IgG and IgA in plasma and mucosal secretions of mice following systemic or mucosal immunization with lymphocytic choriomeningitis virus (LCMV), a widely used experimental model of viral infection. While there are early differences in humoral responses depending on the route of viral entry, we show that both routes generate comparably robust viral-specific IgG in plasma, vaginal, lung, and nasal secretions of immune mice. In contrast, LCMV elicited poor viral-specific IgA responses. Mice that were infected IN showed elevated viral-specific IgA in nasal and lung washes compared to IP-infected mice; however, LCMV-specific IgG overwhelmingly contributed to the humoral response in all mucosal secretions examined. Thus similarly to HIV-1, and several other mucosally-encountered microbial infections, these data suggest that LCMV infection fails to induce vigorous viral-specific IgA responses.

Ubiquitous lens alpha-, beta-, and gamma-crystallins accumulate in anuran cornea as corneal crystallins.

Corneal epithelium is known to have high levels of some metabolic enzymes such as aldehyde dehydrogenase in mammals, gelsolin in zebrafish, and alpha-enolase in several species. Analogous to lens crystallins, these enzymes and proteins are referred to as corneal crystallins, although their precise function is not established in any species. Although it is known that after lentectomy, the outer cornea undergoes transdifferentiation to regenerate a lens only in anuran amphibians, major proteins expressed in an anuran cornea have not been identified. This study therefore aimed to identify the major corneal proteins in the Indian toad (Bufo melanostictus) and the Indian frog (Rana tigrina). Soluble proteins of toad and frog corneas were resolved on two-dimensional gels and identified by matrix-assisted laser desorption ionization time-of-flight/time-of-flight and electrospray ionization quadrupole time-of-flight. We report that anuran cornea is made up of the full complement of ubiquitous lens alpha-, beta-, and gamma-crystallins, mainly localized in the corneal epithelium. In addition, some taxon-specific lens crystallins and novel proteins, such as alpha- or beta-enolase/tau-crystallin, were also identified. Our data present a unique case of the anuran cornea where the same crystallins are used in the lens and in the cornea, thus supporting the earlier idea that crystallins are essential for the visual functions of the cornea as they perform for the lens. High levels of lens alpha-, beta-, and gamma-crystallins have not been reported in the cornea of any species studied so far and may offer a possible explanation for their inability to regenerate a lens after lentectomy. Our data that anuran cornea has an abundant quantity of almost all the lens crystallins are consistent with its ability to form a lens, and this connection is worthy of further studies.

Stability, homodimerization, and calcium-binding properties of a single, variant betagamma-crystallin domain of the protein absent in melanoma 1 (AIM1).

AIM1 (absent in melanoma), a candidate suppressor of malignancy in melanoma, is a nonlens member of the betagamma-crystallin superfamily, which contains six predicted betagamma domains. The first betagamma-crystallin domain of AIM1 (AIM1-g1) diverges most in sequence from the superfamily consensus. To examine its ability to fold and behave like a normal betagamma domain, we cloned AIM1-g1 and overexpressed it in Escherichia coli as a recombinant protein. The recombinant domain was found to be a stable, soluble protein, similar to lens protein gammaBeta-crystallin in secondary structure. The tertiary structure of AIM1-g1 is dominated by the contribution of aromatic amino acids and cysteine. AIM1-g1 undergoes concentration-independent, noncovalent homodimerization with no trace of monomer, similar to a one-domain protein spherulin 3a. Since many betagamma domain proteins bind calcium, we have also investigated the calcium-binding properties of AIM1-g1 by various methods. AIM1-g1 binds the calcium-mimic dye Stains-all, the calcium probe terbium (with K(D) 170 microM), and (45)Ca when blotted on a membrane. AIM1-g1 binds calcium (K(D) 30 microM) with a comparatively higher affinity than bovine lens gamma-crystallin (90 microM). However, calcium binding does not induce significant change in the protein conformation in the near- and far-UV CD and in fluorescence. The AIM1-g1 domain is as stable as domains of betagamma-crystallins (betaB2- or gammaS-crystallins) as monitored by guanidinium chloride unfolding (midpoint of unfolding transition is 1.8 M GdmCl), and the stability of the protein is not altered upon binding calcium as evaluated by equilibrium unfolding. These results show that, despite the sequence variation, AIM1-g1 folds such as a betagamma domain, binds calcium and undergoes dimerization.