Section 2. The main office of a bank shall be in the town specified in its charter or in its agreement of association or in such other town to which the office has been lawfully moved or to which it may be moved as provided in this section. The location of the main office of a bank may be changed to a point in the town of its location or to another town within the commonwealth with the written consent of the commissioner. The business conducted by a bank at its main office shall include not less than 1 of the following transactions: receiving deposits; paying withdrawals; or making loans.