Rab Interacting Molecules 2 and 3 Directly Interact with the Pore-Forming CaV1.3 Ca2+ Channel Subunit and Promote Its Membrane Expression

Rab interacting molecules (RIMs) are multi-domain proteins that positively regulate the number of Ca²⁺ channels at the presynaptic active zone (AZ). Several molecular mechanisms have been demonstrated for RIM-binding to components of the presynaptic Ca²⁺ channel complex, the key signaling element at the AZ. Here, we report an interaction of the C₂B domain of RIM2α and RIM3γ with the C-terminus of the pore-forming α-subunit of Ca_V1.3 channels (Ca_V1.3α1), which mediate stimulus-secretion coupling at the ribbon synapses of cochlear inner hair cells (IHCs). Co-expressing full-length RIM2α with a Ca²⁺ channel complex closely resembling that of IHCs (Ca_V1.3α1-Ca_Vß2a) in HEK293 cells doubled the Ca²⁺-current and shifted the voltage-dependence of Ca²⁺ channel activation by approximately +3 mV. Co-expression of the short RIM isoform RIM3γ increased the Ca_V1.3α1-Ca_Vß2a-mediated Ca²⁺-influx in HEK293 cells, but disruption of RIM3γ in mice left Ca²⁺-influx in IHCs and hearing intact. In conclusion, we propose that RIM2α and RIM3γ directly interact with the C-terminus of the pore-forming subunit of Ca_V1.3 Ca²⁺ channels and positively regulate their plasma membrane expression in HEK293 cells.

Nanobiotechnology advanced antifouling surfaces for the continuous electrochemical monitoring of glucose in whole blood using a lab-on-a-chip

In the current work we have developed a lab-on-a-chip containing embedded amperometric sensors in four microreactors that can be addressed individually and that are coated with crystalline surface protein monolayers to provide a continuous, stable, reliable and accurate detection of blood glucose. It is envisioned that the microfluidic device will be used in a feedback loop mechanism to assess natural variations in blood glucose levels during hemodialysis to allow the individual adjustment of glucose. Reliable and accurate detection of blood glucose is accomplished by simultaneously performing (a) blood glucose measurements, (b) autocalibration routines, (c) mediator-interferences detection, and (d) background subtractions. The electrochemical detection of blood glucose variations in the absence of electrode fouling events is performed by integrating crystalline surface layer proteins (S-layer) that function as an efficient antifouling coating, a highly-oriented immobilization matrix for biomolecules and an effective molecular sieve with pore sizes of 4 to 5 nm. We demonstrate that the S-layer protein SbpA (from Lysinibacillus sphaericus CCM 2177) readily forms monomolecular lattice structures at the various microchip surfaces (e.g. glass, PDMS, platinum and gold) within 60 min, eliminating unspecific adsorption events in the presence of human serum albumin, human plasma and freshly-drawn blood samples. The highly isoporous SbpA-coating allows undisturbed diffusion of the mediator between the electrode surface, thus enabling bioelectrochemical measurements of glucose concentrations between 500 μM to 50 mM (calibration slope δI/δc of 8.7 nA mM(-1)). Final proof-of-concept implementing the four microfluidic microreactor design is demonstrated using freshly drawn blood. Accurate and drift-free assessment of blood glucose concentrations (6. 4 mM) is accomplished over 130 min at 37 °C using immobilized enzyme glucose oxidase by calculating the difference between autocalibration (10 mM glc) and background measurements. The novel combination of biologically-derived nanostructured surfaces with microchip technology constitutes a powerful new tool for multiplexed analysis of complex samples.