Regulation of Phosphatidylinositol Phosphate Kinases: Plant-Specific PIPmodulins

磷脂酰肌醇磷酸5-激酶（PIPKs）是合成PtdIns（4，5）P2的酶，PtdIns（4，5）P2是在植物和动物中发现的重要信号脂质。最近的比较生物化学特性使一个令人信服的论点，植物PIPKs是独特的，多功能的蛋白质，定义植物磷脂酰肌醇（PI）信号。 与哺乳动物的PIPKs不同，拟南芥PIPK 1（AtPIPK 1）直接与肌动蛋白结合，而不需要接头蛋白。此外，AtPIPK 1具有延伸的N-末端结构域，其结合带负电荷的脂质，包括PtdIns（4，5）P2。合成和螯合PtdIns（4，5）P2的能力使其成为最终的PIP调节蛋白，该蛋白被预测为螯合和调节PtdIns（4，5）P2对细胞生理学的影响。没有其他生物（包括哺乳动物、酵母、C.线虫和果蝇）具有包含类似N-末端基序或直接结合肌动蛋白的PIPK。 待检验的假设是植物特异性PIPKs将膜脂质连接到精细肌动蛋白丝，并且高渗胁迫影响这种连接和PIPKs的活性。这项工作将揭示这些植物特异性酶将肌动蛋白细胞骨架连接到细胞膜并产生PtdIns（4，5）P2富集微区的机制的新见解。这项研究将对理解植物和动物中PI代谢的根本差异产生重大影响。这项研究还将影响一名博士后，一名研究生和至少3名本科生的职业生涯，他们将与该小组合作。本科生将获得独立的研究项目，以产生和表征重组蛋白，并将帮助转化原生质体。本科生将为年度全校竞赛撰写研究提案，并将在本科生研究研讨会上展示他们的研究成果。PI项目的本科生通常会因他们的演讲而获奖。此外，该计划的几位年轻科学家已经进入植物生物学领域。

Phosphatidylinositol phosphate 5-kinases (PIPKs) are the enzymes that synthesize PtdIns(4,5)P2, an important signaling lipid found in plants and animals. Recent comparative biochemical characterizations make a compelling argument that plant PIPKs are unique, multifunctional proteins which define plant phosphoinositide (PI) signaling. In contrast to mammalian PIPKs, Arabidopsis PIPK1 (AtPIPK1) binds directly to actin without needing adaptor proteins. Furthermore, AtPIPK1 has an extended N-terminal domain that binds negatively charged lipids including PtdIns(4,5)P2. The ability to both synthesize and sequester PtdIns(4,5)P2 makes this the ultimate PIPmodulin, a protein predicted to sequester and modulate the impact of PtdIns(4,5)P2 on cellular physiology. No other organism (including mammals, yeast, C. elegans and Drosophila) has PIPKs that contain similar N-terminal motifs or that bind directly to actin. The hypothesis to be tested is that the plant-specific PIPKs connect membrane lipids to fine actin filaments and that hyperosmotic stress affects both this connection and the activity of the PIPKs. This work will reveal new insights into the mechanisms through which these plant-specific enzymes connect the actin cytoskeleton to membranes and generate PtdIns(4,5)P2-enriched microdomains.The research will have a major impact on the understanding of the fundamental differences in PI metabolism in plants and animals. The research also will impact the careers of one postdoc, one graduate student and at least 3 undergraduates a semester who will work with the group. The undergraduates will be given independent research projects to generate and characterize the recombinant proteins and will help with transforming protoplasts. The undergraduates will write research proposals for the annual University-wide competition and will give a poster presentation on their research at the undergraduate research symposium. Undergraduates in the PIs program routinely win awards for their presentations. Moreover several young scientists from the program have entered into careers in plant biology.