Cooperativity and Flexible Domains Participation in PIP Aquaporin Gating

CANESSA FORTUNA, A.; ZERBETTO, G.; SCOCHERA, F.; VITALI, V.; GONZALEZ FLECHA, F. L; ALLEVA, K.; JOZEFKOWICZ, C.; SOTO, G.

San Francisco

Congreso; 62 Annual Meeting Biophysical Society; 2018

Biophysical Society

From structural data two distinct mechanisms have been proposed to describehow aquaporins are gated (Frick et al. FEBSLett. 2013). Gating of some aquaporins-AQP0 or AQPZ- is mediated by the displacement of a single residueinside the pore (pinching), while for others -e.g. PIP- the blocking of the poreoccurs as the result of loopD rearrangement (capping). Regarding PIP cappingmechanism, it has been suggested that the open-closed transition not only involvesloopD but also N and C-terminal movements. The PIP subfamily consistsof two paralogs, PIP1 and PIP2, which can form heterotetramers.Heterotetramerization occurs with random stoichiometry and all formedheterotetramers have different water transport capability and pH0,5 thanPIP2 homotetramers (Jozefkowicz et al. Biophys J. 2016). Since there is nostructural information available for PIP1, many of the molecular events thatexplain changes in the pH sensing in heterotetramers are still unknown.We investigate the cooperative gating of homo and heterotetramers. Inparticular, we study the participation of flexible domains in this process.Our results show that all homo and heterotetrameric species share the samedegree of cooperativity for proton sensing. However the cooperativity isapparently lower when PIP1-PIP2 heterotetramers and PIP2 homotetramersare both present in the membrane due to their different pH0,5. In addition,we detected loopD participation in PIP2 gating is more efficient than Cterm,since mutation of Leu202 keep the channel open even at low pH, whiletruncation of C-term do not modify pH sensing. The elucidation of the peculiaritiesof PIP gating sheds light on the regulatory mechanisms that controlwater transport trough membranes and extends the knowledge about theparticipation of flexible domains in the control of the biological activity ofoligomeric channels.