Nonclassical protein secretion by bacteria.

自由生活的微生物必须能够感知、理解、响应和利用它们的外部环境。显微镜下的单细胞细菌通常对外界环境有非常灵活和多样的反应。有些是机会致病菌，因此它们可以在接触到宿主生物体时立即感知并感染它;另一些则进化出了利用最难消化的食物来源的方法。甲壳素是继纤维素之后地球上第二丰富的天然聚合物。甲壳素存在于昆虫和甲壳类动物的外骨骼以及真菌中，甲壳素是N-乙酰氨基葡萄糖（GlcNAc）的线性链，完全不溶，非常坚韧和稳定。一些细菌已经找到了如何利用甲壳素作为生长的碳源和氮源。它们将不同的几丁质酶分泌到细胞外，这些几丁质酶在细胞外共同作用，将几丁质分解成GlcNAc二糖。然后这些被吸收到细胞中并转化为葡萄糖，氨和乙酸。为了使这个系统发挥作用，几丁质酶必须首先在细胞内产生，然后分泌到细胞外。细菌如何做到这一点是这项研究计划的主题。如果我们能发现他们是怎么做到的，也许我们能让他们做得更多。这将使我们能够将食物垃圾加工成生物燃料或其他化学品。一些医学科学家也认为分泌的几丁质酶可能有助于病原体感染宿主，因此找出如何阻止酶分泌的发生也可能对社会有价值。在导致这一建议的工作中，我们已经在一种名为粘质沙雷氏菌的细菌中发现了几丁质酶分泌所必需的基因。这种细菌分布广泛，研究充分，主要是因为它可能导致医疗保健获得性感染。几丁质酶分泌系统涉及一组位于细胞被膜中的蛋白质，包围细胞，以及控制细胞壁渗透性以允许几丁质酶排出的酶。这个研究项目将找出这个系统是如何工作的，因为目前没有人知道。

Free-living microbes must be able to sense, make sense of, respond to, and exploit their outside environment. Microscopic, single-celled bacteria often have very nimble and varied responses to the outside environment. Some are opportunistic pathogens, so they can immediately sense when they have come into contact with a host organism and should infect it. Others have evolved ways to utilise even the most recalcitrant food sources that may be present. Chitin is, after cellulose, the second-most abundant natural polymer on Earth. Present in insect and crustacean exoskeletons, as well as in fungi, chitin is a linear chain of N-Acetyl Glucosamine (GlcNAc) and is completely insoluble and incredibly tough and stable.Some bacteria have figured out how to use chitin is a carbon and nitrogen source for growth. They secrete different chitinase enzymes all the way out of the cell and, working together outside, these chitinases breakdown the chitin into GlcNAc disaccharides. These are then taken up into the cell and converted to glucose, ammonia and acetic acid. For this system to work, the chitinases must be first made inside the cell and then secreted outside. How bacteria do this is the subject of this research proposal. If we can find out how they do it, maybe we can make them do it more. This will enable us to process food waste into biofuels or other chemicals. Some medical scientists also think that secreted chitinases may help pathogens infect their hosts, so figuring out how to stop enzyme secretion happening may also be of value to society.In work leading to this proposal we have found the genes essential for chitinase secretion in a bacterium called Serratia marcescens. This bacterium is widespread and well studied, mostly because it can be responsible for heathcare-acquired infections. The chitinase secretion system involves a set of proteins that reside in the cell envelope, surrounding the cell, and an enzyme that controls the permeability of the cell wall to allow the chitinases out. This research project will find out how the system works because nobody knows at the moment.