El-Kirat-Chatel Sofiane, Beaussart Audrey, Vincent Stéphane P, Abellán Flos Marta, Hols Pascal, Lipke Peter N, Dufrêne Yves F
Université catholique de Louvain, Institute of Life Sciences, B-1348 Louvain-la-Neuve, Belgium.
Nanoscale. 2015 Feb 7;7(5):1760-7. doi: 10.1039/c4nr06315e.
In the baker's yeast Saccharomyces cerevisiae, cell-cell adhesion ("flocculation") is conferred by a family of lectin-like proteins known as the flocculin (Flo) proteins. Knowledge of the adhesive and mechanical properties of flocculins is important for understanding the mechanisms of yeast adhesion, and may help controlling yeast behaviour in biotechnology. We use single-molecule and single-cell atomic force microscopy (AFM) to explore the nanoscale forces engaged in yeast flocculation, focusing on the role of Flo1 as a prototype of flocculins. Using AFM tips labelled with mannose, we detect single flocculins on Flo1-expressing cells, showing they are widely exposed on the cell surface. When subjected to force, individual Flo1 proteins display two distinct force responses, i.e. weak lectin binding forces and strong unfolding forces reflecting the force-induced extension of hydrophobic tandem repeats. We demonstrate that cell-cell adhesion bonds also involve multiple weak lectin interactions together with strong unfolding forces, both associated with Flo1 molecules. Single-molecule and single-cell data correlate with microscale cell adhesion behaviour, suggesting strongly that Flo1 mechanics is critical for yeast flocculation. These results favour a model in which not only weak lectin-sugar interactions are involved in yeast flocculation but also strong hydrophobic interactions resulting from protein unfolding.
在面包酵母酿酒酵母中，细胞间黏附（“絮凝”）由一类称为絮凝蛋白（Flo）的凝集素样蛋白赋予。了解絮凝蛋白的黏附特性和机械特性对于理解酵母黏附机制很重要，并且可能有助于在生物技术中控制酵母行为。我们使用单分子和单细胞原子力显微镜（AFM）来探索酵母絮凝过程中涉及的纳米级力，重点关注Flo1作为絮凝蛋白原型的作用。使用标记有甘露糖的AFM探针，我们在表达Flo1的细胞上检测到单个絮凝蛋白，表明它们广泛暴露在细胞表面。当受到力作用时，单个Flo1蛋白表现出两种不同的力响应，即弱凝集素结合力和反映疏水串联重复序列力诱导延伸的强解折叠力。我们证明细胞间黏附键还涉及多个弱凝集素相互作用以及与Flo1分子相关的强解折叠力。单分子和单细胞数据与微观尺度的细胞黏附行为相关，强烈表明Flo1的力学特性对酵母絮凝至关重要。这些结果支持这样一种模型，即酵母絮凝不仅涉及弱凝集素 - 糖相互作用，还涉及蛋白质解折叠产生的强疏水相互作用。
