Prolyl-4 hydroxylase (P4H) is an enzyme that catalyzes the hydroxylation of proline residues which is a modification of biological importance. P4H in certain organisms exist as a catalytic monomer. In the case of mussels, P4H assumes a tetrameric α₂β₂ configuration. A catalytic domain (CAT) responsible for modifying mussel foot proteins (Mfp) exists in the a-subunit. Hydroxyproline is stated to be an important modification for Mfps to form structurally stable and adhesive threads that the mussel uses to adhere to underwater surfaces. This study presents a novel method to engineer a monomeric P4H to modulate catalytic activity towards mussel-like substrates. It is shown that mutations in binding loops (loop mutants) results in soluble and purifiable constructs that retain catalytic activity. Designed loop mutants showed small levels of substrate conversion up to 3-5h. Sustained consumption up to 23h was not observed. While substrate consumption decayed at later time points, accumulation of multi-modified product was observed. Prolonged accumulation of multi-modified substrates suggested that designed mutants may have had higher affinity for substrates already modified. Loop mutants remained less active as compared to wild type. Additionally, larger mutants were designed by fusing core P4H to a peptide substrate binding (PSB) domain. Using fusion with both a native linker-domain and engineered glycine-4-serine linker, PSB fusions were unsuccessfully purified.