title: A gastrolith protein serving a dual role in the formation of an amorphous mineral containing extracellular matrix.
abstract: Despite the proclamation of Lowenstam and Weiner that crustaceans are the "champions of mineral mobilization and deposition of the animal kingdom," relatively few proteins from the two main calcification sites in these animals, i.e., the exoskeleton and the transient calcium storage organs, have been identified, sequenced, and their roles elucidated. Here, a 65-kDa protein (GAP 65) from the gastrolith of the crayfish, Cherax quadricarinatus, is fully characterized and its function in the mineralization of amorphous calcium carbonate (ACC) of the extracellular matrix is demonstrated. GAP 65 is a negatively charged glycoprotein that possesses three predicted domains: a chitin-binding domain 2, a low-density lipoprotein receptor class A domain, and a polysaccharide deacetylase domain. Expression of GAP 65 was localized to columnar epithelial cells of the gastrolith disk during premolt. In vivo administration of GAP 65 dsRNA resulted in a significant reduction of GAP 65 transcript levels in the gastrolith disk. Such gene silencing also caused dramatic structural and morphological deformities in the chitinous-ACC extracellular matrix structure. ACC deposited in these gastroliths appeared to be sparsely packed with large elongated cavities compared with the normal gastrolith, where ACC is densely compacted. ACC spherules deposited in these gastroliths are significantly larger than normal. GAP 65, moreover, inhibited calcium carbonate crystallization in vitro and stabilized synthetic ACC. Thus, GAP 65 is the first protein shown to have dual function, involved both in extracellular matrix formation and in mineral deposition during biomineralization.
authors.affiliation: Department of Life Sciences, Ben Gurion University of the Negev, Beer-Sheva 84105, Israel.
authors.forename: Assaf
authors.initials: A
authors.lastname: Shechter
authors.forename: Lilah
authors.initials: L
authors.lastname: Glazer
authors.forename: Shira
authors.initials: S
authors.lastname: Cheled
authors.forename: Eyal
authors.initials: E
authors.lastname: Mor
authors.forename: Simy
authors.initials: S
authors.lastname: Weil
authors.forename: Amir
authors.initials: A
authors.lastname: Berman
authors.forename: Shmuel
authors.initials: S
authors.lastname: Bentov
authors.forename: Eliahu D
authors.initials: ED
authors.lastname: Aflalo
authors.forename: Isam
authors.initials: I
authors.lastname: Khalaila
authors.forename: Amir
authors.initials: A
authors.lastname: Sagi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003400:Astacoidea; D002119:Calcium Carbonate / Q000737:chemistry*; D002686:Chitin / Q000737:chemistry; D004247:DNA / Q000235:genetics / Q000502:physiology*; D005109:Extracellular Matrix / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000737:chemistry; D020869:Gene Expression Profiling; D020868:Gene Silencing; D008855:Microscopy, Electron, Scanning; D008903:Minerals / Q000737:chemistry*; D008954:Models, Biological; D008969:Molecular Sequence Data; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D016326:Extracellular Matrix Proteins; D008903:Minerals; D012333:RNA, Messenger; D002686:Chitin; D004247:DNA; D002119:Calcium Carbonate