Department of Biology, Microbial Ecology Group, Lund University, Ecology Building, SE-223 62 Lund, Sweden.
Centre for Environmental and Climate Research (CEC), Lund University, Ecology Building, SE-223 62 Lund, Sweden.
Environ Sci Technol. 2020 Apr 21;54(8):5121-5130. doi: 10.1021/acs.est.0c00860. Epub 2020 Apr 6.
Proteins are a substantial nitrogen source in soils provided that they can be hydrolyzed into bioavailable small peptides or amino acids. However, the strong associations between proteins and soil minerals restrict such proteolytic reactions. This study focused on how an extracellular fungal protease ( sp.) hydrolyzed iron oxide-associated bovine serum albumin (BSA) and the factors that affected the proteolysis. We combined batch experiments with size-exclusion and reversed phase liquid chromatography and infrared spectroscopic measurements to monitor the generation of proteolytic products in solution as well as the real-time changes of the adsorbed BSA during 24 h. Results showed that protease hydrolyzed the iron oxide-associated BSA directly at the surface without an initial desorption of BSA. Concurrently, the protease was adsorbed to vacant surface sites at the iron oxides, which significantly slowed down the rate of proteolysis. This inhibiting effect was counteracted by the presence of preadsorbed phosphate or by increasing the BSA coverage, which prevented protease adsorption. Fast initial rates of iron oxide-associated BSA proteolysis, comparable to proteolysis of BSA in solution, and very slow rates at prolonged proteolysis suggest a large variability in mineral-associated proteins as a nitrogen source in soils and that only a fraction of the protein is bioavailable.
蛋白质是土壤中重要的氮素来源，只要它们能被水解成可利用的小肽或氨基酸。然而，蛋白质与土壤矿物质之间的强相互作用限制了这种蛋白水解反应。本研究集中于一种细胞外真菌蛋白酶（sp.）如何水解氧化铁结合的牛血清白蛋白（BSA），以及影响蛋白水解的因素。我们结合批实验、排阻和反相液相色谱以及红外光谱测量来监测溶液中蛋白水解产物的生成以及 24 小时内吸附 BSA 的实时变化。结果表明，蛋白酶直接在表面上水解氧化铁结合的 BSA，而无需 BSA 的初始解吸。同时，蛋白酶被吸附到氧化铁上的空位表面，这显著降低了蛋白水解的速率。这种抑制作用可以通过存在预吸附的磷酸盐或通过增加 BSA 的覆盖度来抵消，这可以防止蛋白酶的吸附。氧化铁结合的 BSA 蛋白水解的初始速率很快，与溶液中 BSA 的蛋白水解相当，而在长时间的蛋白水解过程中速率非常缓慢，这表明矿物质结合蛋白作为土壤中氮素来源具有很大的可变性，并且只有一部分蛋白质是可利用的。
