Review Question - QID 210900

A 4-year-old boy is brought to his pediatrician by his parents because he has been experiencing recurrent nosebleeds. He always seemed to bleed a lot with minor cuts and scrapes; however, since starting preschool 1 month ago he has had several prolonged nosebleeds. His teacher was concerned about the duration of these episodes and recommended he be medically evaluated. He has otherwise been healthy and there is no family history of bleeding disorders. Physical exam reveals scattered petechial rashes. Labs are obtained with the following results:

Bleeding time: 12 minutes (normal 2-7 minutes)
Partial thromboplastin time: 29 seconds (normal 25-40 seconds)
Prothrombin time: 14 seconds (normal 11-15 seconds)

A peripheral blood smear in shown in Figure A. The protein that is most likely defective in this patient most likely bind to which of the following?