{"id":5864,"date":"2025-01-31T12:12:24","date_gmt":"2025-01-31T18:12:24","guid":{"rendered":"https:\/\/www.vanderbilt.edu\/csb\/?p=5864"},"modified":"2025-01-31T12:12:24","modified_gmt":"2025-01-31T18:12:24","slug":"investigations-into-inositol-phosphates-the-mtor-regulators-youve-never-heard-of","status":"publish","type":"post","link":"https:\/\/www.vanderbilt.edu\/csb\/2025\/01\/31\/investigations-into-inositol-phosphates-the-mtor-regulators-youve-never-heard-of\/","title":{"rendered":"Investigations into inositol phosphates: the mTOR regulators you\u2019ve never heard of!"},"content":{"rendered":"
\"\"
Ray Blind, Medicine<\/figcaption><\/figure>\n

Inositol phosphates are a family of small metabolites characterized by their different phosphorylation patterns. Inositol hexakisphosphate (IP6<\/sub>), the fully phosphorylated form of inositol phosphate, is found in many organisms and is the most abundant inositol phosphate in animal and plant cells. IP6<\/sub> serves a wide range of functions including regulation of enzyme activity, mediation of protein-protein binding\/oligomerization, and functioning as a structural cofactor. In cryo-electron microscopy and crystallography studies, IP6<\/sub> has been shown to cocrystallize with the protein mTOR (mechanistic target of rapamycin). mTOR is a serine\/threonine kinase which, along with mLST8 and Raptor, make up the nutrient-sensing mTORC1 (mechanistic target of rapamycin complex 1). IP6<\/sub> binds to a highly positive pocket in mTOR formed by the FAT domain and referred to as the I-site. While the FAT domain is known to participate in the conformational changes of kinase activation, contradictory studies have failed to elucidate the exact role played by IP6<\/sub> in mTOR kinase activity.<\/p>\n

Recent work from collaborators Ray Blind<\/a>, Lucia Rameh and John York aims to put these debates to rest by investigating the impact of inositol phosphate species on mTOR function, both alone and in the context of mTORC1.<\/p>\n

The authors first performed autokinase assays using recombinant N-terminal truncated mTOR by itself or co-expressed with LST8 and Raptor. The proteins were incubated for 1 hour with radiolabeled-ATP in the presence or absence of inositol phosphate species and assessed for phosphate incorporation. IP6<\/sub>, IP5<\/sub>, and IP4<\/sub> all increased phosphate incorporation into mTOR and mTORC1 but no other inositol phosphate or inositol demonstrated a large effect. Similarly, IP6<\/sub>, IP5<\/sub>, and IP4<\/sub> also all increased phosphorylation of 4EBP peptides, an mTORC1 substrate, in a concentration-dependent manner. \"\"<\/a>Further, IP6<\/sub> was shown to increase the solubility of mTOR. Under normal conditions, only 16% of mTOR remained soluble after 30 minutes at 30\u00b0C, but the addition of IP6<\/sub> to the mix resulted in 64% of mTOR still in solution after the same amount of time.<\/p>\n

To determine how IP6<\/sub> affects mTOR activity toward exogenous peptide, the authors next assessed enzyme kinetics with various concentrations of ATP. IP6<\/sub> decreased the apparent Km<\/sub> and increased the VMAX<\/sub> for mTOR alone, but did not impact kinetics for mTOR in complex with LST8 and Raptor. Specifically, the presence of IP6<\/sub> stabilized an active conformation of mTOR with a higher affinity for ATP, resulting in the increased rate of catalysis. As mTORC1 is more stable than mTOR alone, this likely accounts for the difference in IP6<\/sub> effects. However, during prolonged reactions (4-16 hours) the presence of IP6<\/sub> does increase mTORC1 product formation, indicating IP6<\/sub> also stabilizes mTORC1 in an active state, although to lesser effect. Finally, the authors demonstrated that the effects of IP6<\/sub> are reversible and IP6<\/sub> dissociates from mTOR when diluted out, consistent with the ability of mTOR to dynamically respond to IP6<\/sub> levels.<\/p>\n

Overall, this work has provided the first comprehensive analysis of inositol phosphate regulation of mTOR and mTORC1, increasing our kinetic understanding of mTOR kinase activity and providing a tool to modulate mTOR\/mTORC1 in cells.<\/p>\n

Read more about this exciting new work in the Journal of Biological Chemistry<\/a>! ~ Cameron I. Cohen<\/em><\/p>\n

 <\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Inositol phosphates are a family of small metabolites characterized by their different phosphorylation patterns. Inositol hexakisphosphate (IP6), the fully phosphorylated form of inositol phosphate, is found in many organisms and is the most abundant inositol phosphate in animal and plant cells. IP6 serves a wide range of functions including regulation of enzyme activity, mediation of…<\/p>\n","protected":false},"author":1185,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"spay_email":"","jetpack_publicize_message":"","jetpack_is_tweetstorm":false,"jetpack_publicize_feature_enabled":true},"categories":[1],"tags":[],"acf":[],"jetpack_featured_media_url":"","jetpack_publicize_connections":[],"jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.vanderbilt.edu\/csb\/wp-json\/wp\/v2\/posts\/5864"}],"collection":[{"href":"https:\/\/www.vanderbilt.edu\/csb\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.vanderbilt.edu\/csb\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.vanderbilt.edu\/csb\/wp-json\/wp\/v2\/users\/1185"}],"replies":[{"embeddable":true,"href":"https:\/\/www.vanderbilt.edu\/csb\/wp-json\/wp\/v2\/comments?post=5864"}],"version-history":[{"count":7,"href":"https:\/\/www.vanderbilt.edu\/csb\/wp-json\/wp\/v2\/posts\/5864\/revisions"}],"predecessor-version":[{"id":5873,"href":"https:\/\/www.vanderbilt.edu\/csb\/wp-json\/wp\/v2\/posts\/5864\/revisions\/5873"}],"wp:attachment":[{"href":"https:\/\/www.vanderbilt.edu\/csb\/wp-json\/wp\/v2\/media?parent=5864"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.vanderbilt.edu\/csb\/wp-json\/wp\/v2\/categories?post=5864"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.vanderbilt.edu\/csb\/wp-json\/wp\/v2\/tags?post=5864"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}