What is different about the HbS gene?
on the surface, there is a valine. Hydrophobic is looking for a pocket to hide in.
Changes the result in a small hydrophobic pocket. As long as nothing wants to bind, you're okay.
However, unnatural interactions lead to clumping, precipate can't go trough the capillaries. So, they burst.
Valine finds a pocket and binds into the pocket--> the two subunits are stuck together, then 3 and 4 get stuck--> no longer soluble