tailieunhanh - Short hydrogen bonds in proteins

The creation of Trichet bonds will result in various advantages both in comparison to the present unstable situation and other proposed solutions. First, the long duration of Trichet bonds will eliminate the immediate crisis caused by short term expiration of significant amounts of debt which is looming over Greece, Ireland, Portugal, Spain and possibly other EU countries. Second, the guarantee of the principal with the zero-coupon ECB bond collateral increases the quality of the Trichet Bonds compared to existing sovereign debt. Third, the market for the new Trichet Bonds will be liquid and likely to trade at appreciating prices as refinancing (roll-over) risk is reduced and time. | FEBS Journal Short hydrogen bonds in proteins Sathyapriya Rajagopal and Saraswathi Vishveshwara Molecular Biophysics Unit Indian Institute of Science Bangalore India Keywords short hydrogen bonds donor-acceptor of backbone side chain secondary structural and residue frequency geometrical constraint hydrogen bond strength Correspondence Molecular Biophysics Unit Indian Institute of Science Bangalore Karnataka 560012 India Fax 91 80 23600535 Tel 91 80 22932611 E-mail sv@ Received 5 December 2004 revised 23 January 2005 accepted 8 February 2005 doi Short hydrogen bonds are present in many chemical and biological systems. It is well known that these short hydrogen bonds are found in the active site of enzymes and aid enzyme catalysis. This study aims to systematically characterize all short hydrogen bonds from a nonredundant dataset of protein structures. The study has revealed that short hydrogen bonds are commonly found in proteins and are widely present in different regions of the protein chain such as the backbone or side chain and in different secondary structural regions such as helices strands and turns. The frequency of occurrence of donors and acceptors from the charged side chains as well as from the neutral backbone atoms is equally high. This suggests that short hydrogen bonds in proteins occur either due to increased strength or due to geometrical constraints and this has been illustrated from several examples. The unique tertiary structures of proteins depend crucially on hydrogen bonds. Extensive investigations carried out on protein structures have shown that the bulk of hydrogen bonds in proteins belong to the normal type with neutral electronegative atoms as proton donors and acceptors 1-3 . The availability of a large number of high-resolution protein crystal structures in the last two decades however has revealed a variety of other types of hydrogen bonds such as C-H-X hydrogen bonds 4-6 hydrogen .