The Advisory Board on Physician Assistants shall consist of five members to be appointed by the Governor as follows: three members shall be licensed physician assistants who have practiced their professions in Virginia for not less than three years prior to their appointments; one shall be a physician who collaborates with at least one physician assistant; and one shall be a citizen member appointed from the Commonwealth at large. Appointments shall be for four-year terms. Vacancies occurring other than by expiration of term shall be filled for the unexpired term. No person shall be eligible to serve on the Advisory Board for more than two successive terms.