As part of the KICSTOR complex functions in the amino acid- sensing branch of the TORC1 signaling pathway. Recruits, in an amino acid-independent manner, the GATOR1 complex to the lysosomal membranes and allows its interaction with GATOR2 and the RAG GTPases. Functions upstream of the RAG GTPases and is required to negatively regulate mTORC1 signaling in absence of amino acids. In absence of the KICSTOR complex mTORC1 is constitutively localized to the lysosome and activated. The KICSTOR complex is also probably involved in the regulation of mTORC1 by glucose (PubMed:28199306, PubMed:28199315). May play a role in the cellular response to oxidative stress (By similarity). {ECO:0000250|UniProtKB:A2A9C3, ECO:0000269|PubMed:28199306, ECO:0000269|PubMed:28199315}. This is the function of Ensembl gene identifier ENSG00000198198 (SZT2, SZT2 subunit of KICSTOR complex).