Nonribosomal peptide synthetase; part of the gene cluster that mediates the biosynthesis of the fusahexin, a cyclic hydrophobic hexapeptide with the amino acid sequence cyclo-(D-Ala-L-Leu-D-allo-Thr-L-Pro-D-Leu-L-Leu) that plays an important role in cell surface hydrophobicity (PubMed:22862913, PubMed:34292732). Fusahexin might also play a role in virulence, sensitivity to osmotic stress and oxidative stress (PubMed:34292732). NRPS4 is the only enzyme within the cluster and its 5 catalytic modules are sufficient to produce fusahexin (PubMed:34292732). The modules 1 to 4 incorporate respectively D-alanine, L-leucine, D-allo-threonine, and L-proline, which is supported by the presence of epimerase domains in modules 1 and 3, which incorporate D-amino acids (PubMed:34292732). The terminal module is responsible for incorporation of the two adjacent leucine units, where the epimerase domain is only used to convert the first unit to D-leucine (PubMed:34292732). The terminal condensation domain (Ct) is involved in cyclization with D-alanine and thereby releasing of fusahexin (PubMed:34292732). Secondary metabolite biosynthesis. NRP synthetases are composed of discrete domains (adenylation (A), thiolation (T) or peptidyl carrier protein (PCP) and condensation (C) domains) which when grouped together are referred to as a single module. Each module is responsible for the recognition (via the A domain) and incorporation of a single amino acid into the growing peptide product. Thus, an NRP synthetase is generally composed of one or more modules and can terminate in a thioesterase domain (TE) that releases the newly synthesized peptide from the enzyme. Occasionally, methyltransferase domains (responsible for amino acid methylation) are present within the NRP synthetase. NRPS4 has the following architecture: A-T-E-C-A-T-C-A-T-E-C-A-T-C-A-T-E-C-T-Ct. Does not affect conidiation but results in reduction of cell surface hydrophobicity. Belongs to the NRP synthetase family.