Browsing by Author "Williamson, M. K."
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- Characterization of osteocalcin (BGP) and matrix gla protein (MGP) fish specific antibodies: validation for immunodetection studies in lower vertebratesPublication . Simes, D; Williamson, M. K.; Schaff, Brian J.; Gavaia, Paulo J.; Ingleton, P. M.; Price, P. A.; Cancela, LeonorIn fish species the basic mechanisms of bone development and bone remodeling are not fully understood. The classification of bone tissue in teleosts as cellular or acellular and the presence of transitional states between bone and cartilage and the finding of different types of cartilage in teleosts not previously recognized in higher vertebrates emphasizes the need for a study on the accumulation of the Gla-containing proteins MGP and BGP at the cellular level. In the present study, polyclonal antibodies developed against BGP and MGP from A. regius (a local marine teleost fish) and against MGP from G. galeus (a Pacific Ocean shark), were tested by Western blot for their specificity against BGP and MGP from several other species of teleost fish and shark. For this purpose we extracted and purified both proteins from various marine and freshwater teleosts, identified them by N-terminal amino acid sequence analysis and confirmed the presence of gamma- carboxylation in the proteins with the use of a stain specific for Gla residues. Each antibody recognized either BGP or MGP with no cross-reaction between proteins detected. All purified fish BGPs and MGPs tested were shown to be specifically recognized, thus validating the use of these antibodies for further studies.
- Gla-rich protein (GRP), a new vitamin K-dependent protein identified from sturgeon cartilage and highly conserved in vertebratesPublication . S B Viegas, Carla; Simes, D; Laizé, Vincent; Williamson, M. K.; Price, P. A.; Cancela, LeonorWe report the isolation of a novel vitamin K-dependent protein from the calcified cartilage of Adriatic sturgeon (Acipenser nacarii). This 10.2-kDa secreted protein contains 16 -carboxyglutamic acid (Gla) residues in its 74-residue sequence, the highest Gla percent of any known protein, and we have therefore termed it Gla-rich protein (GRP). GRP has a high charge density (36 negative 16 positive 20 net negative) yet is insoluble at neutral pH. GRP has orthologs in all taxonomic groups of vertebrates, and a paralog (GRP2) in bony fish; no GRP homolog was found in invertebrates. There is no significant sequence homology between GRP and the Gla-containing region of any presently known vitamin K-dependent protein. Forty-seven GRP sequences were obtained by a combination of cDNA cloning and comparative genomics: all 47 have a propeptide that contains a -carboxylase recognition site and a mature protein with 14 highly conserved Glu residues, each of them being carboxylated in sturgeon. The protein sequence of GRP is also highly conserved, with 78% identity between sturgeon and human GRP. Analysis of the corresponding gene structures suggests a highly constrained organization, particularly for exon 4, which encodes the core Gla domain. GRP mRNA is found in virtually all rat and sturgeon tissues examined, with the highest expression in cartilage. Cells expressing GRP include chondrocytes, chondroblasts, osteoblasts, and osteocytes. Because of its potential to bind calcium through Gla residues, we suggest that GRP may regulate calcium in the extracellular environment.
- Matrix gla protein in xenopus laevis: molecular cloning, tissue distribution, and evolutionary considerationsPublication . Cancela, M. Leonor; Ohresser, M. C. P.; Reia, J. P.; S B Viegas, Carla; Williamson, M. K.; Price, P. A.Matrix Gla protein (MGP) belongs to the family of vitamin K-dependent, Gla-containing proteins and in higher vertebrates, is found in the extracellular matrix of mineralized tissues and soft tissues. MGP synthesis is highly regulated at the transcription and posttranscription levels and is now known to be involved in the regulation of extracellular matrix calcification and maintenance of cartilage and soft tissue integrity during growth and development. However, its mode of action at the molecular level remains unknown. Because there is a large degree of conservation between amino,acid sequences of shark and human MGP, the function of MGP probably has been conserved throughout evolution. Given the complexity of the mammalian system, the study of MGP in a lower vertebrate might be advantageous to relate the onset of MGP expression with specific events during development. Toward this goal, MGP was purified from Xenopus long bones and its N-terminal amino acid sequence was determined and used to clone the Xenopus MGP complementary DNA (cDNA) by a mixture of reverse-transcription (RT)- and 5'- rapid amplification of cDNA ends (RACE)-polymerase chain reaction (PCR). MGP messenger RNA (mRNA) was present in all tissues analyzed although predominantly expressed in Xenopus bone and heart and its presence was detected early in development at the onset of chondrocranium development and long before the appearance of the first calcified structures and metamorphosis. These results show that in this system, as in mammals, MGP may be required to delay or prevent mineralization of cartilage and soft tissues during the early stages of development and indicate that Xenopus is an adequate model organism to further study MGP function during growth and development.
- Teleost fish osteocalcin 1 and 2 share the ability to bind the calcium mineral phasePublication . Cavaco, S.; Williamson, M. K.; Rosa, Joana; Roberto, Vania Palma; Cordeiro, O.; Price, P. A.; Cancela, Leonor; Laizé, Vincent; Simes, DThe occurrence of a second osteocalcin (OC2) has been reported in teleost fish, where it coexists with OC1 in some species. While it has been proposed that OC2 gene originated from OC1 through the fish whole-genome duplication event, little information is available on its molecular function and physiological role. The present study brings biological data supporting the presence of OC2 in the mineral phase of teleost fish bone and its association with the mineral phase together with OC1. The occurrence of OC2 forms with different levels of phosphorylation or c-carboxylation, and with amino acid substitutions was observed. Comparative analysis of mature peptide sequences revealed the high conservation existing between OC1 and OC2, in particular within the core c-carboxyglutamic acid domain, and suggests that both protein forms may have the same function, i.e., binding of calcium ions or hydroxyapatite crystals.