The Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, The University of Edinburgh, Edinburgh EH9 3BF, U.K.
School of Biological Sciences, University of the Punjab, Lahore, Pakistan.
Biochem J. 2024 Sep 18;481(18):1221-1240. doi: 10.1042/BCJ20240296.
Cellulosic microfibrils in plant cell walls are largely ensheathed and probably tethered by hydrogen-bonded hemicelluloses. Ensheathing may vary developmentally as hemicelluloses are peeled to enable cell expansion. We characterised a simple method to quantify ensheathed versus naked cellulosic surfaces based on the ability to adsorb a radiolabelled 'cellulose-complementary oligosaccharide', [3H]cellopentaitol. Filter-paper (cellulose) adsorbed 40% and >80% of aqueous 5 nM [3H]cellopentaitol within ∼1 and ∼20 h respectively. When [3H]cellopentaitol was rapidly dried onto filter-paper, ∼50% of it was desorbable by water, whereas after ∼1 day annealing in aqueous medium the adsorption became too strong to be reversible in water. 'Strongly' adsorbed [3H]cellopentaitol was, however, ∼98% desorbed by 6 M NaOH, ∼50% by 0.2 M cellobiose, and ∼30% by 8 M urea, indicating a role for hydrogen-bonding reinforced by complementarity of shape. Gradual adsorption was promoted by kosmotropes (1.4 M Na2SO4 or 30% methanol), and inhibited by chaotropes (8 M urea), supporting a role for hydrogen-bonding. [3H]Cellopentaitol adsorption was strongly competed by non-radioactive cello-oligosaccharides (Cell2-6), the IC50 (half-inhibitory concentration) being highly size-dependent: Cell2, ∼70 mM; Cell3, ∼7 mM; and Cell4-6, ∼0.05 mM. Malto-oligosaccharides (400 mM) had no effect, confirming the role of complementarity. The quantity of adsorbed [3H]cellopentaitol was proportional to mass of cellulose. Of seven cottons tested, wild-type Gossypium arboreum fibres were least capable of adsorbing [3H]cellopentaitol, indicating ensheathment of their microfibrillar surfaces, confirmed by their resistance to cellulase digestion, and potentially attributable to a high glucuronoarabinoxylan content. In conclusion, [3H]cellopentaitol adsorption is a simple, sensitive and quantitative way of titrating 'naked' cellulose surfaces.
植物细胞壁中的纤维素微纤维主要被氢键结合的半纤维素包裹并可能被束缚。随着半纤维素的剥落以实现细胞扩展，包裹可能会随发育而变化。我们描述了一种简单的方法来基于对半纤维素互补寡糖的吸附能力来定量包裹的和裸露的纤维素表面，半纤维素互补寡糖为[3H]纤维戊糖。滤纸（纤维素）在大约 1 小时和大约 20 小时内分别吸附 5 nM [3H]纤维戊糖的 40％和＞80％。当[3H]纤维戊糖迅速干燥到滤纸上时，约 50％的水可使其解吸，而在水性介质中大约 1 天后退火时，吸附变得太强而无法在水中可逆。然而，“强吸附”的[3H]纤维戊糖可以被 6 M NaOH 约 98％解吸，0.2 M 纤维二糖约 50％解吸，8 M 尿素约 30％解吸，表明氢键的作用得到了形状互补的增强。逐渐的吸附是由亲溶物（1.4 M Na2SO4或 30％甲醇）促进的，而由亲电物（8 M 尿素）抑制的，支持氢键的作用。[3H]纤维戊糖的吸附强烈受到非放射性纤维寡糖（Cell2-6）的竞争，IC50（半抑制浓度）高度依赖于大小：Cell2，约 70 mM；Cell3，约 7 mM；而 Cell4-6，约 0.05 mM。麦芽低聚糖（400 mM）没有影响，证实了互补性的作用。吸附的[3H]纤维戊糖的量与纤维素的质量成正比。在所测试的七种棉花中，野生型陆地棉纤维的纤维吸附[3H]纤维戊糖的能力最低，这表明其微纤维表面被包裹，这通过它们抵抗纤维素酶消化得到证实，并且可能归因于高半乳糖阿拉伯木聚糖含量。总之，[3H]纤维戊糖的吸附是一种简单、灵敏和定量测定“裸露”纤维素表面的方法。
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