聚羟基脂肪酸酯纳米微球：结构特征、生物合成及其在生物技术和生物医药领域的应用

聚羟基脂肪酸酯（polyhydroxyalkanoate）PHA 纳米微球是很多微生物在营养失衡的情况下，在体内合成的一种可生物降解的细胞内聚酯，主要作为微生物的碳源及能量储备。天然 PHA 微球的内部是由疏水的聚酯链构成的疏水核心，其外层是由磷脂界膜及膜上嵌入或附着的包括 PHA合酶 PhaC 和 PHA 颗粒相关蛋白 PhaP 等蛋白构成的边界层。PhaC 通过共价键连接在PHA微球表面，而 PhaP 通过疏水相互作用吸附在 PHA 微球表面。通过将外源性功能蛋白与 PhaC 或 PhaP 进行融合表达，在重组微生物体内就能直接合成表面带有功能蛋白的纳米微球复合体。由于该纳米微球在微生物细胞内是以独立的包涵体形式存在，因此通过细胞破碎及离心等方法就能简便、有效地使其从细胞中分离并得以纯化。鉴于 PHA 微球这种表面易被修饰改造的特性，越来越多的功能蛋白通过与 PHA 微球表面蛋白（PhaC 或 PhaP）的融合表达，呈递在了 PHA 微球表面，使其成为一种廉价、高效的蛋白固定化及呈递的新技术。本文在介绍了 PHA 微球的结构特性及生物合成的基础上，着重综述了目前关于功能化 PHA 微球在蛋白纯化、固定化酶、生物分离、靶向递药、疾病诊断、成像技术及新型疫苗开发方面的研究现状及其未来在生物医药等领域的广泛应用前景。

Polyhydroxyalkanoate Nanoparticles: Structure,Biosynthesis, and Applications in Biotechnology and Biomedicine

Polyhydroxyalkanoates (PHAs) are a family of biodegredable polyesters synthesized by a wide range of bacteria as the energy- and carbon-storage materials. PHA nanoparticles are insoluble spherical inclusions in the cytoplasm, which consists primarily of an amorphous, hydrophobic polyester core, surrounded by an outside phospholipid monolayer embedded with various associated proteins such as PHA synthase (PhaC) and PHA granule associate protein Phasin (PhaP). PhaC is covalently linking with PHA polymer chain, whereas PhaP attaches to the PHA nanoparticles through hydrophobic interactions. Therefore,through fusing the target proteins with either PhaC or PhaP, various functionalized PHA nanoparticles with target proteins immobilized on the granule surface could be synthesized by the genetically engineered bacteria. These nanoparticles are water-insoluble inclusions that can be easily and efficiently purified simply through cell disruption and centrifugation. In recent years, a number of bioactive peptides or proteins have been reported to be immobilized on the surface of PHA granules in vivo by recombinant bacteria such as gram-negative Escherichia coli based on this strategy. It provides a powerful but convenient and low-cost technique to achieve specific functionalized PHA nanoparticles which could be applied in many potential areas in the biological and biomedical fields. In this review, the recent investigations on various functionalized PHA nanoparticles were summarized after a simple introduction of the structure and biosynthesis of natural PHA granules, and the current applications of some functional PHA particles in specific areas such as protein purification, enzyme immobilization, bioseperations, targeted drug delivery, diagnostics, imaging and vaccines were also introduced.