Lysosomal LAMP proteins regulate lysosomal pH by direct inhibition of the TMEM175 channelMaintaining a highly acidic lysosomal pH is central to cellular physiology. Here, we use functional proteomics, single-particle cryo-EM, electrophysiology, and in vivo imaging to unravel a key biological function of human lysosome-associated membrane proteins (LAMP-1 and LAMP-2) in regulating lysosomal pH homeostasis. Despite being widely used as a lysosomal marker, the physiological functions of the LAMP proteins have long been overlooked. We show that LAMP-1 and LAMP-2 directly interact with and inhibit the activity of the lysosomal cation channel TMEM175, a key player in lysosomal pH homeostasis implicated in Parkinson's disease. This LAMP inhibition mitigates the proton conduction of TMEM175 and facilitates lysosomal acidification to a lower pH environment crucial for optimal hydrolase activity. Disrupting the LAMP-TMEM175 interaction alkalinizes the lysosomal pH and compromises the lysosomal hydrolytic function. In light of the ever-increasing importance of lysosomes to cellular physiology and diseases, our data have widespread implications for lysosomal biology.
Lsm12 is an NAADP receptor and a two-pore channel regulatory protein required for calcium mobilization from acidic organellesJiyuan Zhang, Xin Guan, Kunal R. Shah et al.|Nature Communications|2021 Abstract Nicotinic acid adenine dinucleotide phosphate (NAADP) is a potent Ca 2+ -mobilizing second messenger which uniquely mobilizes Ca 2+ from acidic endolysosomal organelles. However, the molecular identity of the NAADP receptor remains unknown. Given the necessity of the endolysosomal two-pore channel (TPC1 or TPC2) in NAADP signaling, we performed affinity purification and quantitative proteomic analysis of the interacting proteins of NAADP and TPCs. We identified a Sm-like protein Lsm12 complexed with NAADP, TPC1, and TPC2. Lsm12 directly binds to NAADP via its Lsm domain, colocalizes with TPC2, and mediates the apparent association of NAADP to isolated TPC2 or TPC2-containing membranes. Lsm12 is essential and immediately participates in NAADP-evoked TPC activation and Ca 2+ mobilization from acidic stores. These findings reveal a putative RNA-binding protein to function as an NAADP receptor and a TPC regulatory protein and provides a molecular basis for understanding the mechanisms of NAADP signaling.
Glutamate-activated BK channel complexes formed with NMDA receptorsJiyuan Zhang, Xingang Guan, Qin Li et al.|Proceedings of the National Academy of Sciences|2018 Significance Large-conductance BK channels are dually activated by voltage and Ca 2+ and play a powerful integrative role in regulating cellular excitability and Ca 2+ signaling in neurons. However, BK channels have a requirement of high intracellular free Ca 2+ concentrations for activation under physiological conditions, and the Ca 2+ sources for their activation are not well understood. In this work, we establish that BK channels physically form protein complexes with Ca 2+ -permeable NMDA receptors via their obligatory BKα and GluN1 subunits. The activation mechanism and function of postsynaptic BK channels at synapses remain largely unknown. We found that postsynaptic BK channels in medial perforant path-dentate gyrus granule cell synapses are activated by NMDA receptor-mediated Ca 2+ influx and modulate excitatory synaptic transmission.