The zinc fingers of the small optic lobes calpain bind polyubiquitin

Abstract

The small optic lobes (SOL) calpain is a highly conserved member of the calpain family expressed in the nervous system. A dominant negative form of the SOL calpain inhibited consolidation of one form of synaptic plasticity, non-associative facilitation, in sensory-motor neuronal cultures in Aplysia, presumably by inhibiting cleavage of protein kinase Cs (PKCs) into constitutively active protein kinase Ms (PKMs) (Hu et al. 2017a). SOL calpains have a conserved set of 5-6 N-terminal zinc fingers. Bioinformatic analysis suggests that these zinc fingers could bind to ubiquitin. In this study, we show that both the Aplysia and mouse SOL calpain (also known as Calpain 15) zinc fingers bind ubiquitinated proteins, and we confirm that Aplysia SOL binds poly- but not mono- or diubiquitin. No specific zinc finger is required for polyubiquitin binding. Neither polyubiquitin nor calcium was sufficient to induce purified Aplysia SOL calpain to autolyse or to cleave the atypical PKC to PKM in vitro. In Aplysia, over-expression of the atypical PKC in sensory neurons leads to an activity-dependent cleavage event and an increase in nuclear ubiquitin staining. Activity-dependent cleavage is partially blocked by a dominant negative SOL calpain, but not by a dominant negative classical calpain. The cleaved PKM was stabilized by the dominant negative classical calpain and destabilized by a dominant negative form of the PKM stabilizing protein KIdney/BRAin protein. These studies provide new insight into SOL calpain's function and regulation. Open Data: Materials are available on https://cos.io/our-services/open-science-badges/ https://osf.io/93n6m/.

Isoform Specificity of PKMs during Long-Term Facilitation inAplysiaIs Mediated through Stabilization by KIBRA

“…In Aplysia, KIBRA stabilizes overexpressed PKM Apl II and PKM Apl III, but not PKM Apl I (Hu et al, 2017b). KIBRA-AAA, in which the three residues found to be essential for PKM binding were mutated (Vogt-Eisele et al, 2014), did not stabilize PKM Apl III (Hu et al, 2017b;Hastings et al, 2018) and erased the forms of LTF blocked by DN-PKM Apl III (Hu et al, 2017b), but did stabilize PKM Apl I and did not erase the forms of LTF blocked by DN-PKM Apl I. Do other isoforms of KIBRA stabilize specific PKMs?…”

MRI ofCapn15knockout mice and analysis of Capn 15 distribution reveal possible roles in brain development and plasticity

“…This is most probably due to the lack of conservation of calcium binding residues in the catalytic domain of SOL calpain (2). In addition, while the SOL calpain zinc finger domain binds to polyubiquitin, polyubiquitin alone or together with calcium did not activate SOL calpain (2).…”

“…However, how SOL calpain is activated and the identity of its substrates remains unknown. While calcium can activate classical calpains by binding to their unique classical penta-EF hand domain and their catalytic domain (30) and can also activate atypical calpains such as Tra by binding to the catalytic domain (20), it was shown to have no detectable effect on SOL calpain activity (2). This is most probably due to the lack of conservation of calcium binding residues in the catalytic domain of SOL calpain (2).…”

“…While calcium can activate classical calpains by binding to their unique classical penta-EF hand domain and their catalytic domain (30) and can also activate atypical calpains such as Tra by binding to the catalytic domain (20), it was shown to have no detectable effect on SOL calpain activity (2). This is most probably due to the lack of conservation of calcium binding residues in the catalytic domain of SOL calpain (2). In addition, while the SOL calpain zinc finger domain binds to polyubiquitin, polyubiquitin alone or together with calcium did not activate SOL calpain (2).…”

Open Science Badges in the Journal of Neurochemistry

“…Unfortunately, some authors still refuse to apply for the open science badges, even though no additional effort is required, other than signing the open science disclosure form. However, a number of manuscripts were already awarded with the Open Material Badge(Anderson et al 2018;Baron et al 2018;Dedoni et al 2018;Hastings et al 2018;Hausmann et al 2018;Ho et al 2018;Hopp et al 2018;Hunter et al 2018;Jacob et al 2018;Kanatsu et al 2018;Lautz et al 2018;Saba et al 2018;Saridaki et al 2018;Scholz et al 2018;Sharma et al 2018).…”