Sodium-coupled neutral amino acid transporter 4 (SNAT4, SLC38A4) belongs to the SNAT family of transporters that mediate the transport of neutral amino acids essential for cellular functions. They are classified into two subfamilies - system A and system N. SLC38A4 exhibits functional and regulatory properties of classically defined system A subfamily. It contains 547 amino acid residues with a predicted molecular mass of 55 kDa. SLC38A4 predominantly transports L-alanine followed by L-histidine and L-glutamine. Studies have suggested that SLC38A4 transports amino acids in both sodium-dependent and sodium-independent manner. For tissue distribution, it is primarily expressed in the liver, muscle, and placenta. The topological study has shown that SLC38A4 consists of ten transmembrane segments with both N and C termini facing the extracellular side.
|Basic Information of SLC38A4|
|Protein Name||Sodium-coupled neutral amino acid transporter 4|
|Aliases||Amino acid transporter A3, Na(+)-coupled neutral amino acid transporter 4, Solute carrier family 38 member 4, System A amino acid transporter 3, System N amino acid transporter 3, ATA3, NAT3, SNAT4|
|Organism||Homo sapiens (Human)|
As a member of the amino acid transporter family, SLC38A4 transports abroad range of amino acids which are required for cellular functions. Besides, in the liver, SLC38A4, together with SLC38A2, is important to provide glutamine and alanine as precursors of glucose for gluconeogenesis, especially in the first hours of fasting. Moreover, studies reported a crucial role of SLC38A4 in liver physiology via PI3-kinase signaling pathway. In the placenta, SLC38A4 was reported to be functional in the first-trimester placenta microvillous membrane but had minimal contributions at term. Besides. microvillous and system A have a strong association with abnormal fetal birth weight and that they may play a crucial role in fetal growth and development.
Fig.1 The 10-transmembrane model of SLC38A4.
This study reported the identification of a disulfide bridge formed by cysteine residues 249 and 321 in SNAT4 that played an important role in the substrate transport but had no effect on trafficking of SNAT4 to the cell surface.
This study investigated the regulation of SNAT4 by hepatocyte nuclear factor (HNF4α) and its roles in differentiating hepatocytes. The results showed that SNAT4 functioned downstream of HNF4α and played important roles in liver development through mechanisms of amino acid uptake and protein synthesis.
Using hydrosulfate cross-linking MTS reagents, this study investigated the critical amino acid residue(s) involved in substrate transport function of SNAT4. The findings suggested that residue Cys-232 at the 4th transmembrane domain of SNAT4 influenced substrate transport capacity.
By using chemical labeling, glycosylation, immunofluorescence combined with molecular modeling approaches, this study firstly reported the membrane topological structure of SNAT4.
This study investigated the expression and localization of SNATs, including SNAT1, SNAT2, SNAT4, in human placenta during gestation. The results showed that SMAT4 was located in the microvillous and basal plasma membranes of the syncytiotrophoblast.
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