Biology subjects

Perisic, O.

Publications and source records attributed to Perisic, O..

5 recordsLinked to original sources

bioRxiv2026

Insights into mechanisms of ATM activation via constitutively active mutants

The Ser/Thr kinase ATM orchestrates cellular responses to DNA double-strand breaks (DSBs) and promotes DSB repair by homologous recombination. In this process, ATM is activated by DNA and the MRN (MRE11, RAD50, and NBS1) complex. Here we show that mutations of the conserved PIKK regulatory domain (PRD) within ATMs kinase domain can confer a maximally active state that no longer requires MRN/DNA. In ATM-knockout human cells, the PRD mutants display substantially higher phosphorylation of histone H2AX, KAP1, and CHK2 than wild-type ATM, with or without IR-induced DNA damage. Cryo-EM structures of two PRD mutants each revealed basal or activated conformations depending on bound ligands, suggesting that disrupting the ordered portion of the PRD results in an enzyme poised to transition to the active conformation. However, the identity of the active-site nucleotide is a key driver of the conformational switching. We speculate that this plasticity might be exploited to develop small-molecule ATM modulators for therapeutic applications.

molecular biology↗

bioRxiv2026

Structural basis for a phosphoinositide-driven mTORC2-AKT positive feedback loop

The mammalian target of rapamycin complex 2 (mTORC2) regulates metabolism, growth, survival and cytoskeletal organization, yet its activation mechanism is poorly understood. We show that mTORC2 is directly activated by membranes and our cryo-electron tomography structure of membrane-bound mTORC2 reveals the N-HEAT region of mTOR is at the major membrane interface. mTORC2 is further potently activated by a positive feedback loop involving reciprocal phosphorylation of mTORC2 and its substrate kinase AKT. Cryo-EM structures of dephosphorylated, autophosphorylated and AKT-phosphorylated mTORC2 reveal structural changes in the SIN1 subunit, regulating an autoinhibitory anchor. Reconstitution of the PDK1-AKT-mTORC2 hub on PIP3-containing membranes shows that PDK1/PIP3-dependent AKT activation drives SIN1-T86 phosphorylation, enabling mTORC2 to phosphorylate S473 of AKTs hydrophobic motif, establishing a PI3K-dependent, phosphorylation-driven positive feedback loop at the membrane.

biochemistry↗

bioRxiv2023

Multifocal, multiphenotypic tumours arising from an MTOR mutation acquired in early embryogenesis

Embryogenesis is a vulnerable time. Mutations in developmental cells can result in the wide dissemination of cells predisposed to disease within mature organs. We characterised the evolutionary history of four synchronous renal tumours from a 14-year-old girl, timing their shared origin to a multipotent embryonic cell committed to the right kidney, around 4 weeks post-conception. Their shared MTOR mutation, absent from normal tissues, enhances protein flexibility, which enables a FAT domain hinge to dramatically increase activity of mTORC1 and mTORC2. Developmental mutations, not usually detected in traditional genetic screening, have vital clinical importance in guiding prognosis, targeted treatment, and family screening decisions for paediatric tumours.

cancer biology↗

bioRxiv2023

Paradoxical dominant negative activity of an immunodeficiency-associated activating PIK3R1 variant

PIK3R1 encodes three regulatory subunits of class IA phosphoinositide 3-kinase (PI3K), each associating with any of three catalytic subunits, namely p110, p110{beta} or p110{delta}. Constitutional PIK3R1 mutations cause diseases with a genotype-phenotype relationship not yet fully explained: heterozygous loss-of-function mutations cause SHORT syndrome, featuring insulin resistance and short stature attributed to reduced p110 function, while heterozygous activating mutations cause immunodeficiency, attributed to p110{delta} activation and known as APDS2. Surprisingly, APDS2 patients do not show features of p110 hyperactivation, but do commonly have SHORT syndrome-like features, suggesting p110 hypofunction. We sought to investigate this. In dermal fibroblasts from an APDS2 patient, we found no increased PI3K signalling, with p110{delta} expression markedly reduced. In preadipocytes, the APDS2 variant was potently dominant negative, associating with Irs1 and Irs2 but failing to heterodimerise with p110. This attenuation of p110 signalling by a p110{delta}-activating PIK3R1 variant potentially explains co-incidence of gain-of-function and loss-of-function PIK3R1 phenotypes.

biochemistry↗

bioRxiv2021

Bipartite binding and partial inhibition links DEPTOR and mTOR in a mutually antagonistic embrace

mTORC1 is a kinase complex regulating cell growth, proliferation and survival. Because mis-regulation of DEPTOR, an endogenous mTORC1 inhibitor, is associated with some cancers, we reconstituted mTORC1 with DEPTOR to understand its function. We find that DEPTOR is a unique partial mTORC1 inhibitor that may have evolved to preserve feedback inhibition of PI3K. Counterintuitively, mTORC1 activated by RHEB or oncogenic mutation is much more potently inhibited by DEPTOR. Although DEPTOR partially inhibits mTORC1, mTORC1 prevents this inhibition by phosphorylating DEPTOR, a mutual antagonism that requires no exogenous factors. Structural analyses of the mTORC1/DEPTOR complex showed DEPTORs PDZ domain interacting with the mTOR FAT region, and the unstructured linker preceding the PDZ binding to the mTOR FRB domain. Here we show, in contrast to previous cellular studies, that both the PDZ and linker regions are essential for inhibition, and it is likely that interaction with the FRB is crucial to the unique partial inhibition.

biochemistry↗