The refunding bonds shall be executed for and on behalf of the state by the state treasurer and the secretary of state or their respective deputies. The right of a deputy to so act shall not be limited by any other statute specifying the circumstances under which he may act for his principal. Interest coupons may be executed by affixing thereto the facsimile signature of the official designated to execute them. If an officer whose signature appears on the refunding bonds or attached coupons ceases to be such officer before delivery of the refunding bonds, his signature shall nevertheless be valid and sufficient for all purposes the same as if he had remained in office until delivery.