Search

Search Results

• 1. [Article] Allosteric Mechanism of Water Channel Gating by Ca2+–calmodulin

  Calmodulin (CaM) is a universal regulatory protein that communicates the presence of calcium to its molecular targets and correspondingly modulates their function. This key signaling protein is important ...

  Citation × Citation Citation Abstract Copy Title: Allosteric Mechanism of Water Channel Gating by Ca2+–calmodulin Author: Reichow, Steve, Clemens, Daniel M., Freites, J. Alfredo, Németh-Cahalan, Karin L., Heyden, Matthias, Tobias, Douglas J., Hall, James E., Gonen, Tamir Year: 2013 Calmodulin (CaM) is a universal regulatory protein that communicates the presence of calcium to its molecular targets and correspondingly modulates their function. This key signaling protein is important for controlling the activity of hundreds of membrane channels and transporters. However, our understanding of the structural mechanisms driving CaM regulation of full-length membrane proteins has remained elusive. In this study, we determined the pseudo-atomic structure of full-length mammalian aquaporin-0 (AQP0, Bos Taurus) in complex with CaM using electron microscopy to understand how this signaling protein modulates water channel function. Molecular dynamics and functional mutation studies reveal how CaM binding inhibits AQP0 water permeability by allosterically closing the cytoplasmic gate of AQP0. Our mechanistic model provides new insight, only possible in the context of the fully assembled channel, into how CaM regulates multimeric channels by facilitating cooperativity between adjacent subunits. Title: Allosteric Mechanism of Water Channel Gating by Ca2+–calmodulin Author: Reichow, Steve, Clemens, Daniel M., Freites, J. Alfredo, Németh-Cahalan, Karin L., Heyden, Matthias, Tobias, Douglas J., Hall, James E., Gonen, Tamir Year: 2013 Calmodulin (CaM) is a universal regulatory protein that communicates the presence of calcium to its molecular targets and correspondingly modulates their function. This key signaling protein is important for controlling the activity of hundreds of membrane channels and transporters. However, our understanding of the structural mechanisms driving CaM regulation of full-length membrane proteins has remained elusive. In this study, we determined the pseudo-atomic structure of full-length mammalian aquaporin-0 (AQP0, Bos Taurus) in complex with CaM using electron microscopy to understand how this signaling protein modulates water channel function. Molecular dynamics and functional mutation studies reveal how CaM binding inhibits AQP0 water permeability by allosterically closing the cytoplasmic gate of AQP0. Our mechanistic model provides new insight, only possible in the context of the fully assembled channel, into how CaM regulates multimeric channels by facilitating cooperativity between adjacent subunits. Close

• 2. [Article] AKAP2 Anchors PKA with Aquaporin-0 to Support Ocular Lens Transparency

  A decline in ocular lens transparency known as cataract afflicts 90% of individuals by the age 70. Chronic deterioration of lens tissue occurs as a pathophysiological consequence of defective water and ...

  Citation × Citation Citation Abstract Copy Title: AKAP2 Anchors PKA with Aquaporin-0 to Support Ocular Lens Transparency Author: Gold, Matthew G., Reichow, Steve, O'Neill, Susan E., Weisbrod, Chad R., Langeberg, Lorene K., Bruce, James E., Gonen, Tamir, Scott, John D. Year: 2011 A decline in ocular lens transparency known as cataract afflicts 90% of individuals by the age 70. Chronic deterioration of lens tissue occurs as a pathophysiological consequence of defective water and nutrient circulation through channel and transporter proteins. A key component is the aquaporin-0 (AQP0) water channel whose permeability is tightly regulated in healthy lenses. Using a variety of cellular and biochemical approaches we have discovered that products of the A-kinase anchoring protein 2 gene (AKAP2/AKAP-KL) form a stable complex with AQP0 to sequester protein kinase A (PKA) with the channel. This permits PKA phosphorylation of serine 235 within a calmodulin (CaM)-binding domain of AQP0. The additional negative charge introduced by phosphoserine 235 perturbs electrostatic interactions between AQP0 and CaM to favour water influx through the channel. In isolated mouse lenses, displacement of PKA from the AKAP2–AQP0 channel complex promotes cortical cataracts as characterized by severe opacities and cellular damage. Thus, anchored PKA modulation of AQP0 is a homeostatic mechanism that must be physically intact to preserve lens transparency. Title: AKAP2 Anchors PKA with Aquaporin-0 to Support Ocular Lens Transparency Author: Gold, Matthew G., Reichow, Steve, O'Neill, Susan E., Weisbrod, Chad R., Langeberg, Lorene K., Bruce, James E., Gonen, Tamir, Scott, John D. Year: 2011 A decline in ocular lens transparency known as cataract afflicts 90% of individuals by the age 70. Chronic deterioration of lens tissue occurs as a pathophysiological consequence of defective water and nutrient circulation through channel and transporter proteins. A key component is the aquaporin-0 (AQP0) water channel whose permeability is tightly regulated in healthy lenses. Using a variety of cellular and biochemical approaches we have discovered that products of the A-kinase anchoring protein 2 gene (AKAP2/AKAP-KL) form a stable complex with AQP0 to sequester protein kinase A (PKA) with the channel. This permits PKA phosphorylation of serine 235 within a calmodulin (CaM)-binding domain of AQP0. The additional negative charge introduced by phosphoserine 235 perturbs electrostatic interactions between AQP0 and CaM to favour water influx through the channel. In isolated mouse lenses, displacement of PKA from the AKAP2–AQP0 channel complex promotes cortical cataracts as characterized by severe opacities and cellular damage. Thus, anchored PKA modulation of AQP0 is a homeostatic mechanism that must be physically intact to preserve lens transparency. Close