title: Beta-sheet capping: signals that initiate and terminate beta-sheet formation.
abstract: In the present work, we address the question of whether different amino acids have different beta-sheet initiating and terminating characteristics. Using a large scale analysis of parallel and antiparallel beta-sheets in a non-redundant dataset of proteins, we observed that most of the amino acids show significant under- or over-representation in at least one of the positions at the two ends of beta-sheets, which are denoted as N-cap and C-cap. In addition, based on statistical data and structural comparison, we found that certain amino acids, especially Asp, Asn, Gly and Pro have strong tendencies to block beta-sheet continuation. Hence, we can consider these residues as beta-sheet terminators. It was also proposed that the dipole moments in parallel beta-sheets, whose direction is from C-terminal (partially negative) to N-terminal (partially positive), are much stronger than has previously been suggested. In fact, enhancement of dipole moments in parallel beta-sheets is a result of the positioning of positively charged residues at N-cap and negatively charged residues at C-cap. This enhancement in dipole moment magnitude leads to strengthened dipolar interactions between parallel beta-sheets dipoles and other partners especially alpha-helices dipoles. The results provide an explanation for the antiparallel alignment of parallel beta-sheets with alpha-helices.
authors.affiliation: Department of Biotechnology, College of Science, University of Tehran, Enghelab Avenue, Tehran, Iran.
authors.forename: Fahim
authors.initials: F
authors.lastname: Farzadfard
authors.forename: Nava
authors.initials: N
authors.lastname: Gharaei
authors.forename: Hamid
authors.initials: H
authors.lastname: Pezeshk
authors.forename: Sayed-Amir
authors.initials: SA
authors.lastname: Marashi
mesh_terms: D000465:Algorithms; D000596:Amino Acids / Q000737:chemistry; D003198:Computer Simulation; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015233:Models, Statistical; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D011506:Proteins