tailieunhanh - Báo cáo y học: "The expansin superfamily"

Tuyển tập các báo cáo nghiên cứu về y học được đăng trên tạp chí y học Wertheim cung cấp cho các bạn kiến thức về ngành y đề tài: The expansin superfamily. | Protein family review The expansin superfamily Javier Sampedro and Daniel J Cosgrove Address Department of Biology Pennsylvania State University 208 Mueller Lab University Park PA 16870 USA. Correspondence Daniel J Cosgrove. E-mail dcosgrove 1@ Published 28 November 2005 Genome Biology 2005 6 242 doi gb-2005-6-l2-242 The electronic version of this article is the complete one and can be found online at http 2005 6 12 242 2005 BioMed Central Ltd Summary The expansin superfamily of plant proteins is made up of four families designated a-expansin P-expansin expansin-like A and expansin-like B. a-Expansin and p-expansin proteins are known to have cell-wall loosening activity and to be involved in cell expansion and other developmental events during which cell-wall modification occurs. Proteins in these two families bind tightly to the cell wall and their activity is typically assayed by their stimulation of cell-wall extension and stress relaxation no bona fide enzymatic activity has been detected for these proteins. a-Expansin proteins and some but not all p-expansin proteins are implicated as catalysts of acid growth the enlargement of plant cells stimulated by low extracellular pH. A divergent group of P-expansin genes are expressed at high levels in the pollen of grasses but not of other plant groups. They probably function to loosen maternal cell walls during growth of the pollen tube towards the ovary. All expansins consist of two domains domain l is homologous to the catalytic domain of proteins in the glycoside hydrolase family 45 GH45 expansin domain 2 is homologous to group-2 grass pollen allergens which are of unknown biological function. Experimental evidence suggests that expansins loosen cell walls via a nonenzymatic mechanism that induces slippage of cellulose microfibrils in the plant cell wall. Gene organization and evolutionary history Expansins are plant cell-wall loosening proteins involved in cell enlargement and in