Sagné C, Agulhon C, Ravassard P, Darmon M, Hamon M, El Mestikawy S, Gasnier B, Giros B
Institut National de la Santé et de la Recherche Médicale U-513, CHU Henri Mondor, 8 Rue du Général Sarrail, 94010 Créteil Cedex, France.
Proc Natl Acad Sci U S A. 2001 Jun 19;98(13):7206-11. doi: 10.1073/pnas.121183498. Epub 2001 Jun 5.
In eukaryotic cells, lysosomes represent a major site for macromolecule degradation. Hydrolysis products are eventually exported from this acidic organelle into the cytosol through specific transporters. Impairment of this process at either the hydrolysis or the efflux step is responsible of several lysosomal storage diseases. However, most lysosomal transporters, although biochemically characterized, remain unknown at the molecular level. In this study, we report the molecular and functional characterization of a lysosomal amino acid transporter (LYAAT-1), remotely related to a family of H+-coupled plasma membrane and synaptic vesicle amino acid transporters. LYAAT-1 is expressed in most rat tissues, with highest levels in the brain where it is present in neurons. Upon overexpression in COS-7 cells, the recombinant protein mediates the accumulation of neutral amino acids, such as gamma-aminobutyric acid, l-alanine, and l-proline, through an H+/amino acid symport. Confocal microscopy on brain sections revealed that this transporter colocalizes with cathepsin D, an established lysosomal marker. LYAAT-1 thus appears as a lysosomal transporter that actively exports neutral amino acids from lysosomes by chemiosmotic coupling to the H+-ATPase of these organelles. Homology searching in eukaryotic genomes suggests that LYAAT-1 defines a subgroup of lysosomal transporters in the amino acid/auxin permease family.
在真核细胞中，溶酶体是大分子降解的主要场所。水解产物最终通过特定转运蛋白从这个酸性细胞器输出到细胞质中。该过程在水解或外排步骤的受损会导致多种溶酶体贮积症。然而，大多数溶酶体转运蛋白尽管已进行生化特性鉴定，但在分子水平上仍不清楚。在本研究中，我们报道了一种溶酶体氨基酸转运蛋白（LYAAT-1）的分子和功能特性，它与一类H⁺偶联的质膜和突触囊泡氨基酸转运蛋白有较远的亲缘关系。LYAAT-1在大多数大鼠组织中表达，在脑中表达水平最高，且存在于神经元中。在COS-7细胞中过表达时，重组蛋白通过H⁺/氨基酸同向转运介导中性氨基酸如γ-氨基丁酸、L-丙氨酸和L-脯氨酸的积累。脑切片的共聚焦显微镜检查显示，该转运蛋白与组织蛋白酶D（一种已确定的溶酶体标记物）共定位。因此，LYAAT-1似乎是一种溶酶体转运蛋白，通过与这些细胞器的H⁺-ATP酶进行化学渗透偶联，将中性氨基酸从溶酶体中主动输出。在真核基因组中的同源性搜索表明，LYAAT-1在氨基酸/生长素通透酶家族中定义了一个溶酶体转运蛋白亚组。
