Comparative characterization of putative chitin deacetylases from Phaeodactylum tricornutum and Thalassiosira pseudonana highlights the potential for distinct chitin‐based metabolic processes in diatoms

Abstract

Summary Chitin is generally considered to be present in centric diatoms but not in pennate species. Many aspects of chitin biosynthetic pathways have not been explored in diatoms. We retrieved chitin metabolic genes from pennate (Phaeodactylum tricornutum) and centric (Thalassiosira pseudonana) diatom genomes. Chitin deacetylase (CDA) genes from each genome (PtCDA and TpCDA) were overexpressed in P. tricornutum. We performed comparative analysis of their sequence structure, phylogeny, transcriptional profiles, localization and enzymatic activities. The chitin relevant proteins show complex subcellular compartmentation. PtCDA was likely acquired by horizontal gene transfer from prokaryotes, whereas TpCDA has closer relationships with sequences in Opisthokonta. Using transgenic P. tricornutum lines expressing CDA‐green fluorescent protein (GFP) fusion proteins, PtCDA predominantly localizes to Golgi apparatus whereas TpCDA localizes to endoplasmic reticulum/chloroplast endoplasmic reticulum membrane. CDA‐GFP overexpression upregulated the transcription of chitin synthases and potentially enhanced the ability of chitin synthesis. Although both CDAs are active on GlcNAc5, TpCDA is more active on the highly acetylated chitin polymer DA60. We have addressed the ambiguous characters of CDAs from P. tricornutum and T. pseudonana. Differences in localization, evolution, expression and activities provide explanations underlying the greater potential of centric diatoms for chitin biosynthesis. This study paves the way for in vitro applications of novel CDAs.

Genome-wide identification of chitinase genes in Thalassiosira pseudonana and analysis of their expression under abiotic stresses

“…It has been suggested that these two elements would quickly disappear from the ocean if chitin stopped circulating [14,15]. To date, chitin metabolism has been investigated in two diatom genera, Thalassiosira and Cyclotella, due to the completion of their genome sequencing [16][17][18].…”

Structural and biochemical insights into the catalytic mechanisms of two insect chitin deacetylases of the carbohydrate esterase 4 family

“…Carbohydrate esterase 4 family (CE4) 2 chitin deacetylases (CDAs, EC 3.5.1.41) catalyze the removal of acetyl groups from chitin to form chitosan (1), a polymer of β-(1,4)-linked d -glucosamine residues. CDAs are widely distributed in protists, diatoms, bacteria, fungi, nematodes, and insects (2–8), playing vital roles in chitinous matrix formation and modification (9), as well as in biological attack of fungal pathogens (5, 10). CDAs have been considered promising targets for the design of antifungal, antibacterial, and pest control reagents (2, 11–13).…”

Unique subsite specificity and potential natural function of a chitosan deacetylase from the human pathogen Cryptococcus neoformans

“…In fungi and insects, CDAs may play a role in morphogenesis, whereas bacterial CDAs may contribute to chitin degradation for nutritional purposes. Interestingly, CDAs differ in their regioselectivity when acting on chitin oligomers, yielding products with different degrees of acetylation (DAs) and patterns of acetylation (PAs) (4,12,(15)(16)(17)(18)(19)(20)(21)(22). This suggests that both the DA and PA may influence the biological activities of chitosan oligomers and, possibly, polymers (4,23,24).…”