英文蛋白质结构课堂练习.pptx

66-1Biochemistry66-2Protein GProtein G is a multidomain extracellular protein found in several Streptococcal species.The protein G referred to in this quiz is actually only the B1 domain of one of these proteins.These repeated domains bind to the Fc portion of IgG.There is no structural similarity between these domains and the StrepA protein,which has similar binding properties.66-3Structure of Protein G(front view and side view)1.protein G amino terminus?2.protein G carboxyl terminus?66-4Structure of Protein G(back view)3.-hairpin motif?(2)4.a type I(or common)turn?Which is type I turn that connects -strands at the carboxyl-terminus66-5Structure of Protein G(side view)5.hydrophilic surface of the -helix?6.positive end of an -helical dipole?7.hydrophobic surface on -strands?66-6Structure of Protein G1.A portion of the protein G-sheet is shown without the side-chains and with the backbone displayed as Sticks.Hydrogen bonds are indicated as dashed lines between the -strands.Note that the H-bonds on the left are perpendicular to the chain direction,whereas those on the right are more evenly-spaced,but are set at an angle to the chain direction.The H-bonds between the parallel strands?66-7Structure of Protein G2.A segment of the -helix backbone is shown as Sticks.The Glu27 residue is shown as Ball and Stick and the other side-chains are Wireframe.Click on the atom that donates a hydrogen bond to the backbone C=O of Glu27.66-8Structure of Protein G3.Three residues near the N-terminus of protein G are shown as Ball and Stick:Phe52,Thr53,and Val54.The peptide bond between Thr53 and Val54?66-9Structure of Protein G4.Three residues in the -helix of protein G are shown as Ball and Stick:Ala24,Thr25,and Ala26.Helical geometry is fixed by preferred dihedral angles about these two backbone bonds:(Psi),rotation about the C-C single bond;and (Phi),rotation about the N-C single bond.The or bond of the Thr25 residue?66-10Structure of Protein G5.The display is Spacefill with Structure coloring except that the -helix backbone is shown as Ball and Stick(with a magenta spiral tracing the helix).The location of Thr25 near the N-terminus of the helix is labelled.Pick an-helical residue about 10 from Thr25.66-11Structure of Protein G6.A segment of the -helix backbone is shown as Sticks.The Glu27 residue is shown as Ball and Stick and the other side-chains are Wireframe.Click on the atom that accepts a hydrogen bond from the N-H of Lys28.66-12Structure of Protein G7.The display is Spacefill with Structure coloring except that three strands of the -sheet are shown as Sticks.One strand is shown as Ball and Stick with Thr2 near the N-terminus labeled.Pick a residue on the same -strand as,and about 15 from Thr2.66-13Structure of Protein G1.The C-terminal -hairpin structure is shown with the sidechains of five threonines displayed as Ball and Stick.Distances(in units)between three pairs of these residues are shown as dashed red lines.Pick the most likely of these potential H-bonds that also occurs between residues on the same -strand.66-14Structure of Protein G2.The sidechains on the solvent-exposed surface of the -sheet are shown as Ball and Stick.The remainder of protein G is Wireframe with Structure coloring.Most of the sidechains here are polar.In addition,two are basic.Pick one of these basic sidechains.66-15Structure of Protein G3.The backbone is shown as Sticks with Structure coloring.The sidechains of the aromatic residues(Tyr,Trp,and Phe)are displayed as Ball and Stick and colored CPK.Click on the residue that is responsible for most of the UV absorbance at 280 nm.66-16Structure of Protein G4.The sidechains on the hydrophilic surface of the -sheet are shown as Spacefill.As noted in a previous question,nearly all of these sidechains are polar.In fact,Ile6 is the only apolar sidechain on the solvent-exposed surface of the -sheet.Click on Ile6.66-17Structure of Protein G5.The sidechains of the six aromatic residues are shown as Spacefill.This side view shows how they fill the hydrophobic core between the -helix and -sheet of protein G.Pick a Phe residue.66-18Structure of Protein G6.The sequence of protein G is shown using the one-letter amino acid code.The segments corresponding to secondary structures are indicated with RasMol Structure coloring.From the groups of five amino acids listed below the sequence,pick the group that is not found in protein G.66-19Structure of Protein G7.Protein G is shown in backbone display with RasMol Structure coloring.But someone has tampered with this picture!It shows an impossible path of the polypeptide chain.Pick the position where this impossible backbone topology occurs.