This is an F1 lobe domain consisting of a ubiquitin like fold found in FERM region of Jak-family tyrosine kinases [1]. Multidomain JAK molecules interact with receptors through their FERM and SH2-like domains, triggering a series of phosphorylation events, resulting in the activation of their kinase domains [2]. Overall, the FERM region maintains the typical three-lobed architecture, with an F1 lobe consisting of a ubiquitin-like fold, an F2 lobe consisting of an acyl-CoA binding protein fold, and an F3 lobe consisting of a pleckstrin-homology (PH) fold [3].

1: Crystal Structure of a Complex of the Intracellular Domain of Interferon lambda Receptor 1 (IFNLR1) and the FERM/SH2 Domains of Human JAK1. Zhang D, Wlodawer A, Lubkowski J; J Mol Biol. 2016;428:4651-4668. PMID:27725180

2: Crystal Structure of the FERM-SH2 Module of Human Jak2. McNally R, Toms AV, Eck MJ; PLoS One. 2016;11:e0156218. PMID:27227461

3: The Janus Kinase (JAK) FERM and SH2 Domains: Bringing Specificity to JAK-Receptor Interactions. Ferrao R, Lupardus PJ; Front Endocrinol (Lausanne). 2017;8:71. PMID:28458652