A common African polymorphism abolishes tyrosine sulfation of human anionic trypsinogen (PRSS2)

Human pancreatic trypsinogens undergo post-translational sulfation on Tyr154, catalysed by the Golgi-resident enzyme tyrosylprotein sulfotransferase 2. Sequence alignments suggest that the sulfation of Tyr154 is facilitated by a unique sequence context which is characteristically found in primate trypsinogens. In the search for genetic variants that might alter this sulfation motif, we identified a single nucleotide polymorphism (c.457G>C) in the PRSS2 (serine protease 2, human anionic trypsinogen) gene, which changed Asp153 to a histidine residue (p.D153H). The p.D153H variant is common in subjects of African origin, with a minor allele frequency of 9.2%, whereas it is absent in subjects of European descent. We demonstrate that Asp153 is the main determinant of tyrosine sulfation in anionic trypsinogen, as both the natural p.D153H variation and the p.D153N mutation result in a complete loss of trypsinogen sulfation. In contrast, mutation of Asp156 and Glu157 only slightly decrease tyrosine sulfation, whereas mutation of Gly151 and Pro155 has no effect. With respect to the biological relevance of the p.D153H variant, we found that tyrosine sulfation had no significant effect on the activation of anionic trypsinogen or the catalytic activity and inhibitor sensitivity of anionic trypsin. Taken together with previous studies, the observations of the present study suggest that the primary role of trypsinogen sulfation in humans is to stimulate autoactivation of PRSS1 (serine protease 1, human cationic trypsinogen), whereas the sulfation of anionic trypsinogen is unimportant for normal digestive physiology. As a result, the p.D153H polymorphism which eliminates this modification could become widespread in a healthy population.

Phaseolin type and heat treatment influence the biochemistry of protein digestion in the rat intestine

The study aimed to investigate thein vivodigestion ofPhaseolus vulgarisphaseolin types differing in their subunit pattern composition. Diets contained either casein as the sole source of protein or a mixture (1:1) of casein and pure Sanilac (S), Tendergreen (T) or Inca (I) phaseolin either unheated or heated. Rats were fed for 11 d with the experimental diets. Their ileal content and mucosa were collected and prepared for electrophoresis, Western blotting, densitometry and MS. Differences in digestion among native phaseolin types were observed for intact phaseolin at molecular weights (MW) of 47–50·5 kDa and for an undigested fragment at MW of 19–21·5 kDa in ileal digesta. In both cases, the concentration of these protein bands was lower for I phaseolin than for S or T phaseolin (P < 0·05). In the mucosa, the concentration of a protein band at MW of 20·5–21·5 kDa was lower for S phaseolin as compared to T or I phaseolin (P < 0·001). The presence of phaseolin subunits and their fragments was confirmed by Western blotting. MS analysis revealed the presence of undigested α and β subunit fragments from phaseolin and endogenous proteins (anionic trypsin I and pancreatic α-amylase) in ileal digesta. Thermal treatment improved digestion (P < 0·01), acting on both dietary and endogenous protein components. In conclusion, this study provides evidence for differences in intestinal digestion among phaseolin types, S phaseolin being more resistant and I phaseolin more susceptible. These differences were affected by the origin of the phaseolin subunit precursor. Heat treatment enhanced phaseolin digestion.