title: Novel details of calsequestrin gel conformation in situ.
abstract: Calsequestrin (CASQ) is the major component of the sarcoplasmic reticulum (SR) lumen in skeletal and cardiac muscles. This calcium-binding protein localizes to the junctional SR (jSR) cisternae, where it is responsible for the storage of large amounts of Ca(2+), whereas it is usually absent, at least in its polymerized form, in the free SR. The retention of CASQ inside the jSR is due partly to its association with other jSR proteins, such as junctin and triadin, and partly to its ability to polymerize, in a high Ca(2+) environment, into an intricate gel that holds the protein in place. In this work, we shed some light on the still poorly described in situ structure of polymerized CASQ using detailed EM images from thin sections, with and without tilting, and from deep-etched rotary-shadowed replicas. The latter directly illustrate the fundamental network nature of polymerized CASQ, revealing repeated nodal points connecting short segments of the linear polymer.
authors.affiliation: From the Department of Cell Developmental Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6058 and.
authors.forename: Stefano
authors.initials: S
authors.lastname: Perni
authors.forename: Matthew
authors.initials: M
authors.lastname: Close
authors.forename: Clara
authors.initials: C
authors.lastname: Franzini-Armstrong
mesh_terms: D029845:Amphibian Proteins / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D002155:Calsequestrin / Q000737:chemistry* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000737:chemistry / Q000378:metabolism; D009206:Myocardium / Q000737:chemistry / Q000378:metabolism; D055503:Protein Multimerization / Q000502:physiology*; D020836:Protein Structure, Quaternary; D011894:Rana pipiens; D012911:Snakes
chemical_list: D029845:Amphibian Proteins; D002155:Calsequestrin; D002118:Calcium
keywords: Calcium-binding Proteins; Electron Microscopy (EM); Junctional Sarcoplasmic Reticulum; Protein Assembly; Sarcoplasmic Reticulum (SR); Skeletal Muscle
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