A method of increasing secretion of an antibody heavy chain and/or an antibody light chain from an E. coli host cell, comprising culturing an E. coli host cell comprising polynucleotide comprising a first polynucleotide encoding a first signal peptide operably linked to a polynucleotide encoding an antibody heavy chain, wherein the average hydrophobicity of the signal peptide is greater than about 0.5; and a second polynucleotide encoding a second signal peptide operably linked to a polynucleotide encoding an antibody light chain, wherein the average hydrophobicity of the second signal peptide is greater than about 0.5, whereby upon expression of the antibody in a host cell, the heavy and light chains are folded and assembled to form a biologically active antibody, wherein the first and second signal peptide are a variant DsbA signal peptide, wherein the variant DsbA signal peptide comprises a) a mutation at residue L11 and/or S18Y of SEQ ID NO:3, wherein the variant DsbA signal peptide has a greater average hydrophobicity than a wildtype DsbA signal peptide of SEQ ID NO:3, which has an average hydrophobicity of 0.50; or b) a mutation at residue L11 and/or S18Y, wherein the mutation at residue L11 is L11I and wherein the variant DsbA signal peptide has a greater average hydrophobicity than a wildtype DsbA signal peptide of SEQ ID NO:3, which has an average hydrophobicity of 0.50; or c) sequence of SEQ ID NO:13 or 15. a first polynucleotide encoding a first signal peptide operably linked to a polynucleotide encoding an antibody heavy chain, wherein the average hydrophobicity of the signal peptide is greater than about 0.5; and a second polynucleotide encoding a second signal peptide operably linked to a polynucleotide encoding an antibody light chain, wherein the average hydrophobicity of the second signal peptide is greater than about 0.5, whereby upon expression of the antibody in a host cell, the heavy and light chains are folded and assembled to form a biologically active antibody, wherein the first and second signal peptide are a variant DsbA signal peptide, wherein the variant DsbA signal peptide comprises a) a mutation at residue L11 and/or S18Y of SEQ ID NO:3, wherein the variant DsbA signal peptide has a greater average hydrophobicity than a wildtype DsbA signal peptide of SEQ ID NO:3, which has an average hydrophobicity of 0.50; or b) a mutation at residue L11 and/or S18Y, wherein the mutation at residue L11 is L11I and wherein the variant DsbA signal peptide has a greater average hydrophobicity than a wildtype DsbA signal peptide of SEQ ID NO:3, which has an average hydrophobicity of 0.50; or c) sequence of SEQ ID NO:13 or 15. a) a mutation at residue L11 and/or S18Y of SEQ ID NO:3, wherein the variant DsbA signal peptide has a greater average hydrophobicity than a wildtype DsbA signal peptide of SEQ ID NO:3, which has an average hydrophobicity of 0.50; or b) a mutation at residue L11 and/or S18Y, wherein the mutation at residue L11 is L11I and wherein the variant DsbA signal peptide has a greater average hydrophobicity than a wildtype DsbA signal peptide of SEQ ID NO:3, which has an average hydrophobicity of 0.50; or c) sequence of SEQ ID NO:13 or 15.