Improved bacterial secretion signals derived from pelB and ompA are provided. The improved variants enhance bacterial membrane secretion are thus useful for production of proteins secreted from bacteria including proteins displayed on filamentous phage particles, and, in particular, proteins requiring oxidative formation of covalent bonds, such as disulfide bonds within or between polypeptide chains in order to form a correctly folded and functional protein structure. Described herein are methods for the multivalent display of complex dimeric proteins on the surface of a bacteriophage particle and combinatorial synthetic libraries of such proteins displayed as a fusion polypeptide with filamentous phage pIX coat protein. Heterodimeric or more complex interchain bonded structures may also be displayed using the method of the invention.
