Sandbox Reserved 1626: Difference between revisions

The pore-forming subunit of the MCU contains 351 amino acid residues with both the <scene name='83/832952/Matrix_domain/1'>N- and C-terminal domains</scene> [[Image:Electronegativity_MCU_2.jpg|250 px|right|thumb|'''Fig. 1''' View of the entrance of the MCU (from the intermembrane space).]] located in the matrix of the mitochondria.  The two transmembrane domains, <scene name='83/832952/Tm1/1'>TM1</scene> and <scene name='83/832952/Tm2/1'>TM2</scene>, are connected by a solvent- exposed loop with a highly conserved <scene name='83/832952/Starting_scene/3'>DXXE motif</scene> which is essential for the <scene name='83/832952/Calcium/2'>calcium transport</scene>, located in the upper helix of TM2. The first pore-lining residues are <scene name='83/832952/Selectivity_filter_asp/1'>Asp333</scene> and <scene name='83/832952/Selectivity_filter_glu/1'>Glu336</scene>, that are both part of the highly conserved <scene name='83/832952/Starting_scene/3'>DXXE motif</scene> connecting TM1 and TM2. Each monomer has a <scene name='83/832952/Selectivity_filter_glu/1'>Glu336</scene> whose carboxylate group points toward the pore center. The diameter of the ring is 5Å meaning that the calcium is dehydrated. <scene name='83/832952/Tryptophan/1'>Trp332</scene> stabilizes the carboxyl groups of two neighboring <scene name='83/832952/Selectivity_filter_glu/1'>Glu336</scene> residues through hydrogen bonding. The additional interaction of <scene name='83/832952/Tryptophan_proline/1'>Trp 322 with Pro337</scene> serves to orient <scene name='83/832952/Selectivity_filter_glu/1'>Glu336</scene> for calcium coordination. Therefore, <scene name='83/832952/Selectivity_filter_glu/1'>Glu336</scene>, <scene name='83/832952/Tryptophan/1'>Trp332</scene>, and Pro337 make up the highly conserved <scene name='83/832952/Selectivity_filter/1'>selectivity filter/scene>. The high negative character present around the entrance of the MCU (Fig.1) recruits positively charged calcium ions. <ref name="Fan"/>