L07 Chem 481 Lecture Notes - Lecture 7: Coiled Coil, Conformational Isomerism, Protein Folding
13 Dec 2016
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14 September 2016
Lecture 7: Protein Tertiary and Quaternary
I. Proteins
A. Tertiary and Quaternary Protein Structure
1. Basics
a. 3° structure = global conformation including side chain rotamers, 3D structure
b. Can be shown as space filling model with surfaces and shape
• Or as a backbone trace representation with just -carbons
• Backbone + side chain representation (no actual space, filled with side chains)
• Ribbon structure
c. Quaternary structure is when multiple polypeptides assemble to larger complex
• Often shown in tube structure to show the difference between subunits
d. Proteins are classified according to shape and solubility
• Shape: fibrous vs globular proteins
• Solubility: soluble or membrane
e. Fibrous proteins have elongated filaments, most of the polypeptide chain is organized
approximately parallel to a single axis
• Fibrous proteins are usually insoluble in water (form large aggregates)
• Usually play a structural role in nature (both inside and outside cells)
• Aggregation and size make them insoluble
f. Globular proteins are folded into shape, most are soluble in the cytoplasm (“cytoplasmic
soluble proteins”)
• Many membrane proteins are similar in globular shape actually
2. -Keratin
a. Found in hair, fingernails, claws, horns, beaks
b. Sequence consists of 311-314 residue -helical rod segments capped with non-helical N-
and C-termini (non-helical domains)
• Primary structure of helical rods consists of 7-residue repeats (a-b-c-d-e-f-g, where a
and d are nonpolar)
• Interactions among a and d positions promote association of helices
c. helix forms coiled coil of two -helices, then a protofilament (pair of coiled coils), and
finally a filament (four right handed twisted protofibrils)
• The rod domains form coiled coils consisting of intertwined right handed -helices
• The coiled coils then wind around each other in a left-handed twist
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