Protein Trafficking In The Endosomal-Lysosomal System

内体-溶酶体系统中的蛋白质运输

• 批准号: 8351146
• 负责人: JUAN BONIFACINO
• 金额: $ 242.69万
• 依托单位: EUNICE KENNEDY SHRIVER NATIONAL INSTITUTE OF CHILD HEALTH & HUMAN DEVELOPMENT
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8351146
• 关键词: Adaptor Signaling Protein; Alzheimer' s Disease; Amino Acid Sequence; Amino Acids; Amyloid beta-Protein; Amyloid beta-Protein Precursor; Amyotrophic Lateral Sclerosis; Angiopoietin-2; Animal Model; Autophagocytosis; Bacterial Proteins; Binding; Binding Sites; Biochemical; Blood Platelets; C-terminal; Capsid Proteins; Cells; Characteristics; Clathrin; Clathrin Adaptors; Coated vesicle; Collaborations; Complex; Consensus; Defect; Disease; Endopeptidases; Endosomes; Genes; Glutamine; Goals; Hermanski-Pudlak Syndrome; Human; Integral Membrane Protein; Knowledge; Laboratories; Leucine; Location; Lysosomes; Mammalian Cell; Mediating; Melanosomes; Membrane; Molecular; Mus; Mutant Strains Mice; Mutation; Names; Neurodegenerative Disorders; Neurodevelopmental Disorder; Organelles; Pathogenesis; Peptide Sequence Determination; Peptide Signal Sequences; Physiological; Physiological Processes; Plants; Process; Property; Protein Isoforms; Proteins; Regulation; Risk Factors; Roentgen Rays; Role; Signal Transduction; Site; Sorting - Cell Movement; Spain; Structure; Syndrome; System; TFAP2A gene; Tail; Tissues; Toxin; Transcription Factor AP-1; Tyrosine; Ubiquitin; Variant; Vesicle; Work; amyloid precursor protein processing; base; cell type; combinatorial; gamma secretase; human disease; lipid transport; motor neuron degeneration; novel; preference; protein transport; receptor; retrograde transport; trafficking; trans-Golgi Network

We investigate the molecular mechanisms by which transmembrane proteins are sorted to different compartments of the endomembrane system such as endosomes, lysosomes and a group of cell-type-specific organelles known as lysosome-related organelles (e.g., melanosomes and platelet dense bodies). Sorting is mediated by recognition of signals present in the cytosolic domains of the transmembrane proteins by adaptor proteins that are components of membrane coats (e.g., clathrin coats). Among these adaptor proteins are the heterotetrameric AP-1, AP-2, AP-3 and AP-4 complexes, the monomeric GGA proteins, and the heteropentameric retromer complex. Proper sorting requires the function of additional components of the trafficking machinery that mediate vesicle tethering and fusion. Current work in our laboratory is aimed at elucidating the structure, regulation and physiological roles of coat proteins and vesicle tethering factors, and investigating human diseases that result from genetic defects (e.g., Hermansky-Pudlak syndrome; neurodegenerative and neurodevelopmental disorders) of these proteins. AP-1, AP-2, and AP-3 are clathrin-associated adaptor complexes that recognize two types of sorting signal referred to as tyrosine-based and dileucine-based. Previous studies showed that tyrosine-based signals bind to the mu1, mu2 and mu3 subunits, whereas dileucine-based signals bind to a combination (i.e., a hemicomplex) of two subunits, gamma-sigma1, alpha-sigma2 and delta-sigma3, from the corresponding AP complexes. Structure-based mutational analyses allowed us to pinpoint the exact location of the binding sites for dileucine-based sorting signals fitting the DEXXXLLI consensus motif on the AP-1, AP-2 and AP-3 complexes. The location and topography of the corresponding sites are similar, although the strength and amino acid requirements of different interactions depend on the exact sequence of the signal and the particular AP complex involved. We also demonstrated the occurrence of multiple AP-1 complexes resulting from combinatorial assembly of various gamma (i.e., gamma1 and gamma2) and sigma1 (i.e., sigma1A, sigma1B and sigma1C) subunit isoforms encoded by different genes. These AP-1 variants bind dileucine-based signals with marked preferences for certain sequences, implying that they are not functionally equivalent. Indeed, mutations in sigma1A and sigma1B have recently been shown to be the cause of two severe neurodevelopmental disorders known as the MEDNIK and Fried syndromes, respectively. Based on our work, we hypothesize that defects in these diseases are caused by abnormal sorting of specific cargo proteins having dileucine-based signals. The AP-4 complex is distinct from the other AP complexes in that it does not recognize canonical tyrosine-based and dileucine-based signals. We recently found that, instead, the mu4 subunit of AP-4 binds an YKFFE sequence from the cytosolic tail of the Alzheimer's disease amyloid precursor protein (APP). Biochemical and X-ray crystallographic analyses revealed that the properties of the APP sequence and the location of the binding site on mu4 are distinct from those of canonical tyrosine-based signals binding to the mu subunits of other AP complexes. Two APP-like proteins, APLP1 and APLP2, have related sequences that also interact with mu4. Disruption of the AP-4-APP interaction shifts the distribution of APP from endosomes to the trans-Golgi network and enhances gamma-secretase-catalyzed processing of APP to the pathogenic amyloid-beta peptide. These results demonstrate that APP and AP-4 engage in a novel type of signal-adaptor interaction that mediates transport of APP from the trans-Golgi network to endosomes, thereby reducing amyloidogenic processing of the protein. AP-4 should thus be considered a novel regulator of APP processing and trafficking, and a potential risk factor for Alzheimer's disease. In previous work, we found that a complex named GARP is a critical component of the molecular machinery that mediates retrograde transport of various cargo proteins, including sorting receptors, processing endopeptidases, fusogenic proteins and bacterial and plant toxins, from endosomes to the trans-Golgi network in mammalian cells. We showed that the molecular function of this complex is to promote tethering and fusion of endosome-derived transport carriers to the trans-Golgi network. Biochemical analyses showed that the human GARP complex comprises four subunits named Vps52, Vps53, Vps54 and Ang2. Interference with any of the GARP subunits blocks the delivery of many cargos to the trans-Golgi network, leading to global defects in lysosomal function, lipid traffic and autophagy. In collaboration with Aitor Hierro (CIC-bioGUNE, Bilbao, Spain), we solved the crystal structure of a C-terminal fragment from Vps54, the first atomic structure to be solved for any part of the GARP complex. This structure revealed that that GARP is related to other multisubunit tethering complexes such as the exocyst and COG. In addition, we found that a leucine-967 to glutamine substitution in Vps54 identified in the wobbler mouse, an animal model for amyotrophic lateral sclerosis (ALS), destabilizes the protein, leading to lower levels of the GARP complex in all tissues. The motor neuron degeneration that is characteristic of this mutant mouse is therefore due to decreased levels of GARP and the ensuing defects in retrograde transport.

我们研究了跨膜蛋白被分类到膜系统不同区室的分子机制，如核内体、溶酶体和一组被称为溶酶体相关细胞器的细胞类型特异性细胞器（如黑素体和血小板致密体）。分选是通过识别存在于跨膜蛋白细胞质结构域的信号来介导的，这些信号是由作为膜外壳成分的衔接蛋白（例如，网格蛋白外壳）介导的。这些接头蛋白包括异四聚体AP-1、AP-2、AP-3和AP-4复合物、单体GGA蛋白和异四聚体反转录复合物。适当的分类需要转运机制中介导囊泡捆绑和融合的其他成分的功能。我们实验室目前的工作旨在阐明外壳蛋白和囊泡系栓因子的结构、调控和生理作用，并研究由这些蛋白的遗传缺陷（如Hermansky-Pudlak综合征、神经退行性和神经发育障碍）引起的人类疾病。