Vishnu S. Mishra

Hermansky-Pudlak syndrome type 7 (HPS-7) results from mutant dysbindin, a member of the biogenesis of lysosome-related organelles complex 1 (BLOC-1)

Hermansky-Pudlak syndrome (HPS; MIM 203300) is a genetically heterogeneous disorder characterized by oculocutaneous albinism, prolonged bleeding and pulmonary fibrosis due to abnormal vesicle trafficking to lysosomes and related organelles, such as melanosomes and platelet dense granules. In mice, at least 16 loci are associated with HPS, including sandy (sdy; ref. 7). Here we show that the sdy mutant mouse expresses no dysbindin protein owing to a deletion in the gene Dtnbp1 (encoding dysbindin) and that mutation of the human ortholog DTNBP1 causes a novel form of HPS called HPS-7. Dysbindin is a ubiquitously expressed protein that binds to α- and β-dystrobrevins, components of the dystrophin-associated protein complex (DPC) in both muscle and nonmuscle cells. We also show that dysbindin is a component of the biogenesis of lysosome-related organelles complex 1 (BLOC-1; refs. 9–11), which regulates trafficking to lysosome-related organelles and includes the proteins pallidin, muted and cappuccino, which are associated with HPS in mice. These findings show that BLOC-1 is important in producing the HPS phenotype in humans, indicate that dysbindin has a role in the biogenesis of lysosome-related organelles and identify unexpected interactions between components of DPC and BLOC-1.

Does the heterozygous state of alpha-1 antitrypsin deficiency have a role in chronic liver diseases? Interim results of a large case-control study.

Background: The role of the heterozygous PiZ state of alpha-1 antitrypsin deficiency (&agr;1ATD) in the pathogenesis of chronic liver disease (LD) is still a matter of controversy. Aim: To determine the prevalence of &agr;1ATD heterozygote states in a large population of patients with established LD compared with individuals with no LD, and to determine whether the prevalence of PiZ is increased in patients with more severe LD. Methods: A cross sectional case-control study among patients with and without LD. Blood samples were tested for &agr;1AT levels and &agr;1AT phenotype. The severity of LD was determined by clinical evaluation, lab tests, imaging studies and histopathology. Results: In total, 1405 patients were enrolled; 651 with, and 754 without LD. Out of them, 173 patients had decompensated cirrhosis requiring liver transplantation. PiMZ was significantly more prevalent in White patients (3.5%) compared with Hispanics (1.7%; P = 0.029). There was no difference in PiMZ prevalence between the total LD group and the group with no LD (2.1% vs. 1.7%; P = 0.64). Within the LD group, 5.7% of 173 patients with decompensated LD, listed for liver transplantation, had PiMZ, compared with 2.1% of 478 patients with less severe LD (P = 0.016). Similarly, there was a disproportionately higher prevalence of PiZ among hepatitis C virus (HCV) patients (5.6%) and patients with nonalcoholic fatty liver disease (NAFLD) (5.0%) with decompensated LD, compared with HCV patients (1.2%) and NAFLD patients (1.9%) with less severe LD (P = 0.044 and 0.017, respectively). Patients with cryptogenic cirrhosis, who were not considered NAFLD patients, did not have a higher prevalence of PiMZ compared with patients with LD of known etiologies (1.9% vs. 2.3%; P = 0.12). Conclusions: We found no association between the heterozygous PiZ state of &agr;1ATD and the presence of chronic LD in-general or the presence of cryptogenic cirrhosis. In contrast, patients with decompensated LD of any etiology had a significantly higher prevalence of PiMZ compared with patients with compensated LD. Furthermore, in patients with chronic LD due to HCV or NAFLD there was a significant association between the PiMZ heterozygous state and increased severity of LD and the need for liver transplantation. These interim results suggest that the PiMZ &agr;1ATD heterozygous state may have a role in worsening LD due to HCV or NAFLD.

Immunogenicity and sequence analysis of recombinant p58 : a neutralization-sensitive, antigenically conserved Babesia bigemina merozoite surface protein

The gene encoding the conserved, neutralization-sensitive surface protein p58 of Babesia bigemina was cloned and sequenced. An open reading frame of 1440 bases was found to encode a protein with a predicted size of 54 kDa. A transmembrane hydrophobic domain and signal peptide were present at the amino-terminus. The polypeptide encoded by a nearly full length cDNA was expressed in bacteria and contained epitope(s) reactive with anti-p58 polyclonal and monoclonal antibodies. Serum antibodies from rabbits immunized with a lysate of recombinant bacteria specifically immunoprecipitated native p58 from [35S]methionine-labeled B. bigemina antigens. In addition, the sera contained antibodies that bound to the surface of live merozoites from 4 geographically different Latin American isolates, confirming the presence and immunogenicity of conserved, surface-exposed epitopes on the recombinant polypeptide. This molecular clone will now enable immunization trials in cattle designed to better evaluate the ability of p58 to induce immune protection by vaccinating with constructs containing only conserved, neutralization-sensitive epitopes.

A CapG gain‐of‐function mutant reveals critical structural and functional determinants for actin filament severing

CapG is the only member of the gelsolin family unable to sever actin filaments. Changing amino acids 84–91 (severing domain) and 124–137 (WH2‐containing segment) simultaneously to the sequences of gelsolin results in a mutant, CapG‐sev, capable of severing actin filaments. The gain of severing function does not alter actin filament capping, but is accompanied by a higher affinity for monomeric actin, and the capacity to bind and sequester two actin monomers. Analysis of CapG‐sev crystal structure suggests a more loosely folded inactive conformation than gelsolin, with a shorter S1–S2 latch. Calcium binding to S1 opens this latch and S1 becomes separated from a closely interfaced S2–S3 complex by an extended arm consisting of amino acids 118–137. Modeling with F‐actin predicts that the length of this WH2‐containing arm is critical for severing function, and the addition of a single amino acid (alanine or histidine) eliminates CapG‐sev severing activity, confirming this prediction. We conclude that efficient severing utilizes two actin monomer‐binding sites, and that the length of the WH2‐containing segment is a critical functional determinant for severing.

Genetic mapping of vacuolar protein sorting-45 (Vps45) on mouse Chromosome 3

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