TheAspergillus nigerannexin,anxC3.1is constitutively expressed and is not essential for protein secretion

Abstract

An annexin, anxC3.1, was isolated and characterised from the industrially important filamentous fungus Aspergillus niger. anxC3.1 is a single copy gene encoding a 506 amino acid predicted protein which contains four annexin repeats. Disruption of the anxC3.1 gene did not lead to any visible changes in phenotype, nor in the levels of secreted protein, nor specifically in glucoamylase production, suggesting no major role in secretion. anxC3.1 expression was found to be unaltered under a variety of conditions such as increased secretion, altered nitrogen source, heat shock, and decreased Ca2+ levels, indicating that anxC3.1 is constitutively expressed. This is the first reported functional characterisation of a fungal annexin.

Annexin C4 in A. Fumigatus: A proteomics approach to understand the function

“…The sequence analysis of KO cassettes indicated that in both constructs anxC4 ORF was disrupted and the production of a functional protein is unlikely. Previous studies have confirmed the loss of protein function using this disruption approach [7,13]. AnxC4 disruptants did not show any specific phenotype when subjected to various growth conditions.…”

“…The preparation of the anxC4 disruption cassette was as described previously [7]. Briefly, the anxC4 gene of A. fumigatus (~2.7 kb, Afu3g07020, Broad institute) was cloned as an approximately 5 kb PCR product containing 5′ and 3′ flanking regions in pGEM-T Easy vector.…”

“…Little is known about annexins' functions in filamentous fungi. A gene knock out study on anxC3.1 in A. niger demonstrated a non-essential function of this gene in fungal growth and protein secretion [7]. To understand the anxC4 function in human pathogen, A. fumigatus, a knock out strain has been generated in the present study.…”

The enigmatic role of fungal annexins: the case of Cryptococcus neoformans

“…However, sequence analysis revealed no other annexin in C. neoformans and therefore if another molecular player is responsible for redundancy in annexin functions, it could not be readily identified by sequence homology. Our data is similar to what has been previously shown for Aspergillus spp, where no obvious phenotypes were observed upon deletion of annexin genes (13, 15, 16). Likewise, in Neurospora crassa an annexin deleted strain had no gross growth or filamentation defects (40).…”

Annexins

“…This suggests roles in membrane repair, constitutive or stress‐induced autophagy, stromule formation and exo‐/endo‐cytosis. Secretion from the A. niger anxc3.1 mutant appears normal (Khalaj et al. , 2004a), suggesting that other or no annexins participate in exocytosis.…”