Dissecting structural basis of the unique substrate selectivity of human enteropeptidase catalytic subunit

High-Resolution Array Comparative Genomic Hybridization Utility in Polish Newborns with Isolated Cleft Lip and Palate

Cleft lip with or without cleft palate is one of the most common birth defects of unknown etiology. A fraction of its genetic causes is attributable to copy number variations detected by array comparative genomic hybridization. The value of array comparative genomic hybridization screening as a first-tier test in the newborn population with multiple congenital anomalies has now been accepted. Due to unspecific clinical picture at this age, it can also be applied to neonates with isolated anomalies. Our purpose was to assess utility of array comparative genomic hybridization in the population of newborns with isolated cleft lip and palate. We conducted the study in a group of 52 Polish newborns with apparently isolated cleft lip and palate. In the study group, we found 8 rearrangements. Of these, 2 de novo events have been noted that potentially explain the phenotype. In addition, 2 novel candidate genes for cleft lip and palate, CHN2 and CDH19, are suggested. Given the high number of inherited potentially benign changes, we question the clinical utility of array comparative genomic hybridization in the newborn population with isolated cleft lip and palate, at the same time pointing to the need of skilled professional's clinical assessment at a later age. However, the value of this technology in searching for the cause of isolated anomalies cannot be underestimated.

Heterogeneous catalysis on the phage surface: Display of active human enteropeptidase

Enteropeptidase (EC 3.4.21.9) plays a key role in mammalian digestion as the enzyme that physiologically activates trypsinogen by highly specific cleavage of the trypsinogen activation peptide following the recognition sequence D4K. The high specificity of enteropeptidase makes it a powerful tool in modern biotechnology. Here we describe the application of phage display technology to express active human enteropeptidase catalytic subunits (L-HEP) on M13 filamentous bacteriophage. The L-HEP/C122S gene was cloned in the g3p-based phagemid vector pHEN2m upstream of the sequence encoding the phage g3p protein and downstream of the signal peptide-encoding sequence. Heterogeneous catalysis of the synthetic peptide substrate (GDDDDK-β-naphthylamide) cleavage by phage-bound L-HEP was shown to have kinetic parameters similar to those of soluble enzyme, with the respective Km values of 19 μM and 20 μM and kcat of 115 and 92 s(-1). Fusion proteins containing a D4K cleavage site were cleaved with phage-bound L-HEP/C122S as well as by soluble L-HEP/C122S, and proteolysis was inhibited by soybean trypsin inhibitor. Rapid large-scale phage production, one-step purification of phage-bound L-HEP, and easy removal of enzyme activity from reaction samples by PEG precipitation make our approach suitable for the efficient removal of various tag sequences fused to the target proteins. The functional phage display technology developed in this study can be instrumental in constructing libraries of mutants to analyze the effect of structural changes on the activity and specificity of the enzyme or generate its desired variants for biotechnological applications.

Human enteropeptidase light chain: bioengineering of recombinants and kinetic investigations of structure and function

The serine protease enteropeptidase exhibits a high level of substrate specificity for the cleavage sequence DDDDK∼ X, making this enzyme a useful tool for the separation of recombinant protein fusion domains. In an effort to improve the utility of enteropeptidase for processing fusion proteins and to better understand its structure and function, two substitution variants of human enteropeptidase, designated R96Q and Y174R, were created and produced as active (>92%) enzymes secreted by Pichia pastoris with yields in excess of 1.7 mg/Liter. The Y174R variant showed improved specificities for substrates containing the sequences DDDDK (kcat /KM = 6.83 × 10⁶ M⁻¹ sec⁻¹) and DDDDR (kcat /KM = 1.89 × 10⁷ M⁻¹ sec⁻¹) relative to all other enteropeptidase variants reported to date. BPTI inhibition of Y174R was significantly decreased. Kinetic data demonstrate the important contribution of the positively charged residue 96 to extended substrate specificity in human enteropeptidase. Modeling shows the importance of the charge-charge interactions in the extended substrate binding pocket.