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Homework Assignment #8

Questions

1. You are interested in integrin activation and perform mutagenesis studies on

integrin. You find a mutant form of integrin which you call int-act, because the

int-act mutation causes the extracellular domain to exist always in an unfolded

state regardless of the presence or absence of ligand. When you determine the

sequence of int-act, you find that the mutation is in the intracellular domain of

integrin. Explain how this intracellular mutation could affect the conformation of

the extracellular domain of integrin.

2. Your friend, who is an engineering major, is interested in the mechanical

properties of extracellular matrix and wants to study how secreted collagen

molecules assemble into a collagen fiber. As part of his studies, he has been trying

to speed up the rate at which cells can produce the collagen protein and is

considering reducing the size of the propeptide that is attached to the collagen

chain such that it contains only the ER targeting sequence as well as the site for

cleavage of the propeptide. To his surprise, this modification causes collagen to

be degraded inside the cell. Can you explain why?