Interactions ofCandida albicans with bacteria and salivary molecules in oral biofilms

The yeastCandida albicans coaggregates with a variety of streptococcal species, an interaction that may promote oral colonization by yeast cells.C. albicans andCandida tropicalis are the yeasts most frequently isolated from the human oral cavity and our data demonstrate that both these species bind toStreptococcus gordonii NCTC 7869 while two otherCandida species (Candida krusei andCandida kefyr) do not. Adherence ofC. albicans was greatest when the yeast had been grown at 30° C to mid-exponential growth phase. For 21 strains ofC. albicans there was a positive correlation between the ability to adhere toS. gordonii and adherence to experimental salivary pellicle. Whole saliva either stimulated or slightly inhibited adherence ofC. albicans toS. gordonii depending on the streptococcal growth conditions. The results suggest that the major salivary adhesins and coaggregation adhesins ofC. albicans are co-expressed.     

Effects of cytochalasin D on the distribution of actin and ACTH-induced steroidogenesis in cultured embryonic adrenal gland cells from the Pekin duck (Anas platyrhynchos)

Cultured steroidogenic cells derived from the adrenal glands of duck embryos were used to study changes in the distribution of actin associated with the corticotropic responsiveness. Actin-containing components were identified by rhodamine-phalloidin staining. The actin in most of the unstimulated cells occurred as stress fibers that either ran parallel throughout the cell or were present as domains of parallel fibers at angles to one another. When incubated in Krebs-Henseleit buffer containing 1–24 ACTH, the cells released approximately equal amounts of corticosterone and aldosterone. Incubation of the cells in buffer containing cytochalasin D caused the cells to lose their stress fibers, and the actin became distributed at the periphery in what appeared to be fragments of stress fibers and clumps of fibrous material in the central cytoplasm. Although cytochalasin D did not affect the basal output of corticosterone and aldosterone, the 1–24 ACTH-induced rates of both hormones were suppressed significantly. After the cells had been washed in unadulterated buffer, the normal distribution of actin stress fibers was restored and the cells responded normally when incubated in buffer containing 1–24 ACTH. These results suggest that the actin components of the cytoskeleton are important determinants of corticotropin-induced steroidogenic responsiveness.     

Mutations of the tyrosinase gene in patients with oculocutaneous albinism from various ethnic groups in Israel.

We have analyzed the tyrosinase (TYR) gene in 38 unrelated patients with oculocutaneous albinism (OCA), derived from several different ethnic groups of the diverse population of Israel. We detected TYR gene mutations in 23 of the 34 patients with apparent type I (i.e., tyrosinase-deficient) OCA and in none of the patients with other clinical forms of albinism. Among Moroccan Jews with type IA (i.e., tyrosinase-negative) OCA, we detected a highly predominant mutant allele containing a missense substitution, Gly47Asp (G47D). This mutation occurs on the same haplotype as in patients from the Canary Islands and Puerto Rico, suggesting that the G47D mutation in these ethnically distinct populations may stem from a common origin.     

A new ATP-binding fold in actin, hexokinase and Hsc70

One of a cell biologist's favourite occupations is to discover the proteins that perform newly described functions in the cell. Very often lately, this has resulted in the identification of protein families whose related amino acid sequences reflect similar functions, but can proteins with totally unrelated sequences have similar structures and functions? In this review, Ken Holmes, Chris Sander and Alfonso Valencia describe the structural similarities between three well-known proteins that have no readily detectable primary sequence similarities but for which X-ray crystallography has revealed very similar structures. A comparison of their structures provides insights into their common mechanisms of action and into protein evolution, and has been used to detect related proteins in sequence data bases.     

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.