Homework Assignment #8
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?