Isolation of theCHS4gene ofParacoccidioides brasiliensisand its accommodation in a new class of chitin synthases

Abstract

The nucleotide sequence of a chitin synthase gene (PbrCHS4) of the dimorphic fungal human pathogen Paracoccidioides brasiliensis has been determined. A homology search with the deduced amino acid sequence of PbrChs4 (1744 aa) reveals the presence of two distinct domains, an N-terminal domain showing up to 30% homology to myosin motor-like domains and a C-terminal domain with up to 68% homology to chitin synthases, as has been reported for some class V chitin synthases. However, unlike class V chitin synthases with myosin motor-like domains, PbrChs4 does not present characteristic signatures of myosin motor-like domains. Also, although the Chs domain presents the closest homology to other fungal class V enzymes, it is low enough to consider PbrChs4 as belonging to a new class, which we propose as class VII.

Paracoccidioides brasiliensis: chemical and molecular tools for research on cell walls, antifungals, diagnosis, taxonomy

“…PbrCHS1 and PbrCHS2 have similar transcript sizes at around 3.7 kb, while large transcripts of about 6.5 kb and 6.7 kb were observed for PbrCHS4 and PbrCHS5, respectively. The structures of the latter are similar to cmsA from A. nidulans [29,32], which has been proposed as a chitin synthase coupled to a myosin motor-like region. In association with cytoskeletal structures, the myosin region might translocate the newly synthesized chitin molecules to its site of deposition.…”

“…In accordance with the presence of a-1, 3 Chitin synthesis in fungi is a rather complex process, regulated by multigene families encoding chitin synthase isoenzymes, some of them redundant, whose activities may be spatially ordered and otherwise strictly regulated to bring about the fulfillment of the several roles ascribed to them. Based on differences in regions of high sequence conservation, chitin synthases have been organized into seven classes within two domains, whose functional implications are not yet clear in all cases [28][29][30]. Six chitin synthase genes, representing different classes of enzyme (PbrCHS1 in class I, PbrCHS2 in class II, PbrCHS3 in class IV, PbrCHS4 in class VII, PbrCHS5 in class V and PbCHS6 in class VI) are active in P. brasiliensis [29,[31][32][33]; they help in the synthesis of chitin in amounts that comprise 43% of the dry weight of the wall of the pathogenic Y form and 13% of the M cell wall [34].…”

“…In association with cytoskeletal structures, the myosin region might translocate the newly synthesized chitin molecules to its site of deposition. However, PbrChs4p does not possess the P-loop, switch I and switch II domains present in CsmA and conserved among the myosins, a fact that led us to propose a new Class VII to group several chitin synthases with incomplete myosin-motors [29].…”

“…However, differences exist in primary metabolism between mammals and other eukaryotes such as plants, fungi and protozoa [59]. While mammals synthesize C 27 cholestane-based members of the steroid family, pathogenic fungi, protozoa and plants require the presence of endogenous sterols C 28 -C 29 (typically ergosterol and 24-alkyl analogs) which act as essential growth factors for these organisms. The enzyme responsible for the addition of these alkyl groups to carbon C-24 and for the regulation of carbon flow in the sterol pathway is the D (24) -sterol methyl transferase (SMT) [59,60].…”

Myosin Motor-Like Domain of the Class VI Chitin Synthase CsmB Is Essential to Its Functions inAspergillus nidulans

“…9,10) For the past few years, orthologous genes encoding chitin synthases with MMD have been isolated and characterized from filamentous and dimorphic fungi. [14][15][16][17][18][19][20][21][22][23][24][25][26] With the exception of Ashbya gossypii, all ascomycete filamentous fungi the genome sequences of which have been made public possess genes encoding class V and VI chitin synthases with the MMD. However, yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe, and the dimorphic yeast Candida albicans do not possess orthologous genes in their genomes.…”