Solid-State NMR Analysis of Schizosaccharomyces pombe Reveals Role of α-Amylase Family Enzymes in Cell Wall Structure and Function

Abstract

The fission yeast Schizosaccharomyces pombe is a widely employed model organism for studying the eukaryotic cell cycle. Like plants and bacteria, S. pombe must build a cell wall in concert with its cell cycle, but how cell wall-synthesizing and remodeling enzymes mediate this process remains unclear. Here we characterize the functions of Aah1 and Aah3, two related S. pombe -amylases that are putative members of this evolutionarily conserved family of cell wall-modifying proteins. We found that unlike rod-shaped wildtype S. pombe cells, aah1{Delta} aah3{Delta} cells are nearly spherical, grow slowly, have thickened cell walls, and have severe defects in cell separation following cytokinesis. Solid-state NMR spectroscopy analyses of intact wildtype and aah1{Delta} aah3{Delta} cells revealed that aah1{Delta} aah3{Delta} cell walls are rigidified with a significant reduction in the -glucan matrix, characterized by reduced amounts of the major -1,3-glucan and the minor -1,4-glucan within the rigid and mobile phases; this reduction was compensated for by a two-fold increase in {beta}-glucan content. Indeed, viability of aah1{Delta} aah3{Delta} cells depended on {beta}-glucan upregulation and the cell wall integrity pathway that mediates it. While aah1{Delta} aah3{Delta} cells resemble cells with impaired function of the transglycosylation domain of -glucan synthase 1 (Ags1), increased expression of Aah3 does not compensate for impaired Ags1 function or vice-versa. Overall, our data suggest that Aah1 and Aah3 are required in addition to Ags1, likely downstream, for the transglycosylation of -glucan chains to generate fibers of appropriate dimensions to support proper cell morphology, growth, and division. Significance StatementThis study utilized a range of imaging techniques and high-resolution solid-state NMR spectroscopy of intact S. pombe cells to refine our understanding of S. pombe cell wall composition. This study also determined that two related GPI-anchored -amylase family proteins, Aah1 and Aah3, likely act as transglycosylases non-redundantly with an -glucan synthase in the synthesis of -glucan chains of appropriate content and size to support polarized growth and cell division. Our results also highlight the anti-fungal therapeutic potential of GPI-anchored enzymes acting in concert with glucan synthases.