Ultralong complementarity determining regions and uses thereof

Disclosed herein are immunoglobulin constructs comprising at least one immunoglobulin domain or fragment thereof; and a therapeutic polypeptide or derivative or variant thereof attached to or inserted into said immunoglobulin domain. Also provided are immunoglobulin constructs comprising a mammalian immunoglobulin heavy chain comprising at least a portion of a knob domain in the complementarity-determining region 3 (CDR3H) or fragment thereof; and a therapeutic polypeptide attached to or inserted into said knob domain of the CDR3H. Also provided are immunoglobulin constructs comprising a mammalian immunoglobulin heavy chain comprising at least a portion of a stalk domain in the complementarity-determining region 3 (CDR3H) or fragment thereof; and a therapeutic polypeptide attached to or inserted into said stalk domain of the CDR3H. Also described herein are methods and compositions comprising the immunoglobulin constructs described herein for treatment and prevention of a disease or condition in a subject.