Mechanism of amyloid formation during melanosome biogenesis

 描述（由申请人提供）：PMEL是黑素细胞中的关键因子，并在色素沉着途径中起作用，保护我们的皮肤免受皮肤癌的侵害。为此，该蛋白质在黑素体中形成生理性淀粉样基质。这种基质用于沉积黑色素，保护我们的皮肤免受有害的紫外线照射。PMEL是在人类细胞中发现的第一种生理性淀粉样蛋白。它是更著名的病理性、毒性淀粉样蛋白的表亲，与各种不治之症有关，如阿尔茨海默氏病和帕金森氏病、朊病毒疾病、糖尿病和癌症。然而，生理性淀粉样蛋白如PMEL与其病理性对应物共享形成的各个方面和某些途径，并且一些在类似的内吞隔室中组装和/或积累。因此，PMEL是一个有吸引力的模型系统，研究淀粉样蛋白，并另外持有的承诺，揭示黑素细胞和色素沉着生物学的基本秘密。虽然PMEL在早期分泌区室中表现得像传统的膜蛋白，但一旦它到达黑素体，它就释放了巨大的聚集潜力。我们的目标是研究分子如何感知特定的黑素体环境，表征分子的结构转变，以响应这种环境，并研究如何调节该过程。此外，我们试图了解PMEL如何设法组装成淀粉样蛋白，而不产生淀粉样蛋白臭名昭著的毒性。最后，我们建议表征PMEL淀粉样蛋白形成的分子和细胞要求，重点是Rab GTP酶及其效应物在该过程中的作用。在我们的初步结果的背景下，我们已经确定了一个特定的Rab GTdR，其功能似乎是正确的PMEL处理所需的，我们将研究它是如何工作的。我们对促进淀粉样蛋白形成的细胞因子的研究可能会发现参与建立早期黑素体身份的关键分子，这些细胞器为PMEL形成纤维状淀粉样蛋白提供了最佳环境。我们的具体目标是（1）表征PMEL结构域的功能相互作用如何驱动淀粉样蛋白的形成和（2）确定淀粉样蛋白形成的分子和细胞要求。

 DESCRIPTION (provided by applicant): PMEL is a key factor in melanocytes and operates in the pigmentation pathway that protects our skin from skin cancer. To this end, the protein forms a physiological amyloid matrix in melanosomes. This matrix serves for the deposition of the pigment melanin, which shields our skin against hazardous UV irradiation. PMEL was the first physiological amyloid to be discovered in human cells. It is a cousin of the more (in) famous pathological, toxic amyloids linked with various incurable diseases, such as Alzheimer's and Parkinson's Disease, prion diseases, diabetes, and cancer. However, physiological amyloids like PMEL share various aspects and certain pathways of formation with their pathological counterparts and some assemble and/or accumulate in similar endocytic compartments. Thus, PMEL is an attractive model system to study amyloids and additionally holds the promise of revealing fundamental secrets of melanocyte and pigmentation biology. While PMEL behaves like a conventional membrane protein in early secretory compartments, it unleashes a massive potential for aggregation once it arrives in the melanosome. We aim to examine how the molecule senses the specific melanosomal environment, to characterize the structural transitions of the molecule in response to this environment, and to investigate how the process is regulated. Additionally, we seek to understand how PMEL manages to assemble into amyloid without developing the toxicity for which amyloids are notorious. Finally, we propose to characterize the molecular and cellular requirements for PMEL amyloid formation focusing on the role of Rab GTPases and their effectors in the process. In the context of our preliminary results, we already identified one particular Rab GTPase whose function appears to be required for proper PMEL processing and we will investigate how it works. Our search for cellular factors promoting amyloid formation may discover key molecules involved in establishing the identity of early melanosomes, the organelles that provide the optimal environment for PMEL to form fibrous amyloid. Our specific aims are (1) Characterizing how the functional interplay of the PMEL domains drives amyloid formation and (2) Identifying molecular & cellular requirements for amyloid formation.