Bucandin is a novel presynaptic neurotoxin isolated from Bungarus candidus (Malayan krait). It has the unique property of enhancing presynaptic acetylcholine release and represents a family of three-finger toxins with an additional disulfide in the first loop. There are no existing structures from this sub-category of three-finger toxins. The X-ray crystal structure of bucandin has been determined by the Shake-and-Bake direct-methods procedure. The resulting electron-density maps were of outstanding quality and allowed the automated tracing of 61 of the 63 amino-acid residues, including their side chains, and the placement of 48 solvent molecules. The 0.97 A resolution full-matrix least-squares refinement converged to a crystallographic R factor of 12.4% and the final model contains 118 solvent molecules. This is the highest resolution structure of any member of the three-finger toxin family and thus it can serve as the best model for other members of the family. Furthermore, the structure of this novel toxin will help in understanding its unique ability to enhance acetylcholine release. The unique structure resulting from the fifth disulfide bond residing in the first loop improves the understanding of other toxins with a similar arrangement of disulfide bonds.

The human leukocyte antigen (HLA) alleles are extremely polymorphic among ethnic population and the peptide binding specificity varies for different alleles in a combinatorial manner. However, it has been suggested that majority of alleles can be covered within few HLA supertypes, where different members of a supertype bind similar peptides, yet exhibiting distinct repertoires. Since the overlap between different members of a supertype appears to be extensive, it is crucial to develop a framework for grouping alleles into supertypes just from sequence information. In this report, we define sub supertypes, where members show functional overlap with identical repertoire, and describe a strategy to group HLA-A, B and C alleles into different categories of sub supertypes. The strategy grouped 47% of 295 A alleles, 44% of 540 B alleles and 35% of 156 C alleles to just 36, 71 and 18 groups, respectively. The grouping is moderately validated using available binding data. However, the validation is limited due to lack of binding data. Hence, the data presented in this article serve as a framework to test specific functional overlap between alleles. The grouping of HLA alleles into different categories of sub supertypes has profound use in the understanding of antigenic peptide selection, degeneration and discrimination during T-cell mediated immune response. A complete knowledge of this phenomenon finds utility in epitope design for the development of HLA based vaccines and immuno-therapeutics.

We have optimized the genomic DNA extraction method from fresh and dry laminas, as well as fresh and dry corolla lobes of Ixora cultivars. Some woody tropical species such as these contain excessive amounts of phenolic compounds that co-precipitate with DNA resulting in poor or no amplification during the polymerase chain reaction (PCR). Repeated precipitation with CsCl coupled with phenol : chloroform extraction yielded high quality DNA suitable for consistent PCR amplification. The DNA from fresh laminas of 22 cultivars of Ixora was subjected to random amplified polymorphic DNA (RAPD) analysis. Individual taxa could be identified using specific DNA markers from the RAPD profiles. Cluster analysis of data from six primers grouped all 22 cultivars distinctly under two cultivar groups, viz., Ixora Coccinea and I. Javanica. The percentage genetic similarity was calculated for all the cultivars based on the RAPD data. The two cultivar groups and the outgroup plants were also clearly distinguishable with polar ordination using a matrix of genetic dissimilarities (one minus similarity). Our data indicate that besides the use of RAPD markers for identification of particular Ixora cultivars within a germplasm collection, the phylogenetic relationships generated by RAPD analysis may be useful for future breeding programmes.# 1997 Annals of Botany Company

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