Hydrolase and transferase activities of the beta-1,3-exoglucanase of Candida albicans.

The exo-beta-1,3-glucanase of Candida albicans (Exg) has a marked specificity for beta-1,3-glucosidic linkages as judged by the kinetic constants for p-nitophenyl beta-glucoside, beta-linked disaccharides of glucose (laminaribiose, gentiobiose, and cellobiose), oligosaccharides of the laminari series, laminarin and pustulan. The kcat/Km ratios for a series of laminari oligosaccharides from -biose to -heptaose showed that Exg has an extended substrate-binding site which contains at least five binding sites for sugar residues. Binding at position +2 (the third sugar residue) increases the kcat twofold while positions +3 and +4 lower the Km value further and thereby increase the catalytic efficiency. Exg catalyses an efficient transglucosylation reaction with high concentrations of laminari-oligosaccharides which specifically form beta-1,3 linkages and with yields up to 50%. The rate of the transglucosylation is concentration-dependent and can be more than 10 times faster than the hydrolytic reaction with excess donor substrates such as laminaritriose and laminarihexaose. The kinetics of Exg and the predicted substrate-binding site for up to five sugar residues are consistent with a recent structural analysis of the enzyme-binding site.     

Insights into the evolutionary origins of clostridial neurotoxins from analysis of the <Emphasis Type="Italic">Clostridium botulinum</Emphasis> strain A neurotoxin gene cluster

Background  

Clostridial neurotoxins (CNTs) are the most deadly toxins known and causal agents of botulism and tetanus neuroparalytic diseases. Despite considerable progress in understanding CNT structure and function, the evolutionary origins of CNTs remain a mystery as they are unique to Clostridium and possess a sequence and structural architecture distinct from other protein families. Uncovering the origins of CNTs would be a significant contribution to our understanding of how pathogens evolve and generate novel toxin families.     

Genetic variation in South Indian castes: evidence from Y-chromosome, mitochondrial, and autosomal polymorphisms

Background

Major population movements, social structure, and caste endogamy have influenced the genetic structure of Indian populations. An understanding of these influences is increasingly important as gene mapping and case-control studies are initiated in South Indian populations.

Results

We report new data on 155 individuals from four Tamil caste populations of South India and perform comparative analyses with caste populations from the neighboring state of Andhra Pradesh. Genetic differentiation among Tamil castes is low (R_ST = 0.96% for 45 autosomal short tandem repeat (STR) markers), reflecting a largely common origin. Nonetheless, caste- and continent-specific patterns are evident. For 32 lineage-defining Y-chromosome SNPs, Tamil castes show higher affinity to Europeans than to eastern Asians, and genetic distance estimates to the Europeans are ordered by caste rank. For 32 lineage-defining mitochondrial SNPs and hypervariable sequence (HVS) 1, Tamil castes have higher affinity to eastern Asians than to Europeans. For 45 autosomal STRs, upper and middle rank castes show higher affinity to Europeans than do lower rank castes from either Tamil Nadu or Andhra Pradesh. Local between-caste variation (Tamil Nadu R_ST = 0.96%, Andhra Pradesh R_ST = 0.77%) exceeds the estimate of variation between these geographically separated groups (R_ST = 0.12%). Low, but statistically significant, correlations between caste rank distance and genetic distance are demonstrated for Tamil castes using Y-chromosome, mtDNA, and autosomal data.

Conclusion

Genetic data from Y-chromosome, mtDNA, and autosomal STRs are in accord with historical accounts of northwest to southeast population movements in India. The influence of ancient and historical population movements and caste social structure can be detected and replicated in South Indian caste populations from two different geographic regions.     

Diagnosis of Dermatophytosis

Dermatophytoses are infections of the skin, hair or nails caused by dermatophytes. Dermatophytes can induce typical diagnostic clinical lesions (tinea), but can also mimic other dermatoses. Therefore, physicians need to be familiar with the whole spectrum of tinea and must constantly be mindful of possible dermatophytosis. An examination with Wood’s light can be helpful. In superficial lesions, the demonstration of dermatophytes may be achieved by dermatoscopy or laser scanning. An essential step of the following diagnostic procedure is the skilful collection of samples for the proof of fungi. Microscopy of KOH mounts or equivalent preparations produced from infected material and histology are approved methods. The necessary identification of dermatophytes on species level can finally be accomplished by conventional methods based on cultures or by new techniques based on molecular differentiation or MALDI-TOF analysis. These modern methods are clearly on the increase and can considerably improve and accelerate dermatophyte identification.     

The reversible action of alpha-amanitin on nuclear structure and molecular composition

The effects of brief trypsin treatment on cell shape, surface topography, cytoskeletal components and the freeze-fracture distribution of plasma membrane intramembranous particles (PMP) are examined in contact-inhibited 3T3 cells. Untreated 3T3 cells are flat without many surface modifications, have highly organized microfilaments and microtubules and have clusters of PMP. Within seconds of trypsin treatment using a concentration of trypsin used for routine passage numerous zeiotic blebs appear on the cell surface which appear to “cap” or coalesce on the central superior aspect of the cell. In later stages retraction fibers are observed and the cells then round up and detach from the substrate. Using thin section transmission electron microscopy (TEM) the zeiotic blebs are observed and various constituents of the cytosol, including lysosomes, ribosomes, etc. pinch off and are surrounded by plasma membrane. In general there is a profound disruption of microfilaments and cortical microtubules. There is, however, a focal coalescence of microfilaments subjacent to the zones of the “capped” zeiotic blebs and some relative resistance of centriolar associated microtubules to tryptic degradation. Trypsin also causes profound changes in the nucleus which transforms from the normal round shape to a very convoluted and irregular shape. In addition to the zeiotic bleb formation which can be visualized by freeze-fracture the distribution of PMP goes from the normally clustered state to a more uniform distribution following treatment with trypsin. These studies suggest that there may be some coordinated control of the changes in cell surface topography, cytoskeletal components and intramembranous particle distribution.     

Phylogeny and Phytogeography of Eupatorium (Eupatorieae, Asteraceae): Insights from Sequence Data of the nrDNA ITS Regions and cpDNA RFLP

Eupatorium were examined by sequencing the internal transcribed spacers (ITS) of nuclear ribosomal DNA and restriction site analysis of chloroplast DNA. Molecular data provided strong evidence that (1) this genus originated in North America, (2) the genus diverged into three morphological species groups, Eutrochium, Traganthes and Uncasia in North America, and (3) one of the North American Uncasia lineages migrated into temperate Europe and eastern Asia over the Bering land bridge. The estimated divergence times support a late Miocene to early Pliocene migration from North America to Eurasia via the Bering land bridge. A European species was sister to all of the eastern Asian species examined. The disjunct distribution pattern of the genus Eupatorium is incongruent with the classical Arcto-Tertiary geoflora concept. Received 13 September 1999/ Accepted in revised form 4 January 2000