BCH210H1 Lecture Notes - Lecture 16: Sequence Motif, Hydronium, Isomerization

• School: UTSG
• Department: Biochemistry
• Course: BCH210H1
• Professor: Stavroula Andreopoulos

Document Summary

Prototypic membrane protein (e. g. , glycophorin a, with glycosylated residues on the outside, snakes in the membrane, and short tail: using partition coefficients to calculate with precision the hydrophobicity of a given residue (assigning mathematical numbers) Lecture 16 objectives: understand how and why membrane proteins fold the way they do in the bilayer, e. g. , bacteriorhodopsin, show how structure informs function, describe special case of (cid:574)-sheets in membranes. Membrane protein folding: recall that amino acids in membrane-spanning segments are mostly hydrophobic. Problem #1: peptide backbone is highly polar (- n-h, c=o) Peptide protein sequence: amino acids in the membrane are mostly hydrophobic (favilm, backbone itself is quite polar with c=o and n-h bonds. Intramolecular h-bonds (i to i+4) neutralize polar backbone. Helix traverses membrane with minimal disruption of lipid packing. 10-30% of integral proteins have one membrane spanning segment. Single-spanning proteins always cross membrane as an (cid:573)-helix. 20-25 residues required to span 3-4nm (30-40a) thick membrane.