A 10 year-old boy is brought to your office because his mother is concerned about his frequent bouts of sinusitis, pneumonia and skin infections. He has beautiful blue eyes but is unusually sensitive to bright light. Mother reports that there are some relatives with blue eyes and albinism in her extended family. Physical examination is significant for silvery hair, albinism, hepatosplenomegaly, and ecchymosis. Laboratory tests show neutropenia, thrombocytopenia, elevated bleeding time and hypergammaglobulinemia. Pathology report says there are peroxidase-positive giant granules in the neutrophils on peripheral smear. You suspected Chédiak-Higashi syndrome in this boy. Of the following proteins, which is affected in Chédiak-Higashi syndrome?
