(a) A security interest that arises out of a depository's pledge of a security to secure a deposit of public funds by a public entity or an institution of higher education, as defined by Section 61.003, Education Code, is created, attaches, and is perfected for all purposes under state law from the time that the custodian identifies the pledge of the security on the custodian's books and records and issues the trust receipt.
(b) A security interest in a pledged security remains perfected in the hands of a subsequent custodian or permitted institution.