Crystal structure of bovine trypsinogen at 1-8 A resolution. II. Crystallographic refinement, refined crystal structure and comparison with bovine trypsin.

After the correct placement of the trypsinogen molecules within the trigonal trypsinogen crystals (Bode et al. , 1976 a ), the trypsinogen structure has been refined by a constrained crystallographic refinement at 1·8 A resolution. The final R -value is 0·225. The N-terminus, including residues Val 10 to Gly 18, is mobile and projects into solution. Three chain segments forming the specificity pocket in active trypsin and consisting of residues Gly142 to Pro152, GlyA184 to Gly193 and Gly216 to Asn223 show no significant continuous electron density in the final Fourier map. This indicates statistical or thermal disorder of these chain segments in trypsinogen in contrast to active trypsin, where they are fixed and form an interdigitating structural unit (“activation domain”). It is remarkable that five of the seven sites where the trypsinogen chain becomes flexible contain glycine residues. These glycine residues are conserved in vertebrate serine proteases. The conformation of the remaining protein segments in trypsinogen is quite similar to trypsin (Bode & Schwager, 1975 a ) . The mean displacement of all fixed main-chain atoms is 0·22 A. The only residue that is completely differently placed, but still immobilized, is Asp194. Its side-chain is rotated about 170° and binds to HiAfter the correct placement of the trypsinogen molecules within the trigonal trypsinogen crystals (Bode et al. , 1976 a ) , the trypsinogen structure has been refined by a constrained crystallographic refinement at 1·8 A resolution. The final R -value is 0·225. The N-terminus, including residues Val 10 to Gly 18, is mobile and projects into solution. Three chain segments forming the specificity pocket in active trypsin and consisting of residues Gly142 to Pro152, GlyA184 to Gly193 and Gly216 to Asn223 show no significant continuous electron density in the final Fourier map. This indicates statistical or thermal disorder of these chain segments in trypsinogen in contrast to active trypsin, where they are fixed and form an interdigitating structural unit (“activation domain”). It is remarkable that five of the seven sites where the trypsinogen chain becomes flexible contain glycine residues. These glycine residues are conserved in vertebrate serine proteases. The conformation of the remaining protein segments in trypsinogen is quite similar to trypsin (Bode & Schwager, 1975 a ) . The mean displacement of all fixed main-chain atoms is 0·22 A. The only residue that is completely differently placed, but still immobilized, is Asp194. Its side-chain is rotated about 170° and binds to HiAfter the correct placement of the trypsinogen molecules within the trigonal trypsinogen crystals (Bode et al. , 1976 a ) , the trypsinogen structure has been refined by a constrained crystallographic refinement at 1·8 A resolution. The final R -value is 0·225. The N-terminus, including residues Val 10 to Gly 18, is mobile and projects into solution. Three chain segments forming the specificity pocket in active trypsin and consisting of residues Gly142 to Pro152, GlyA184 to Gly193 and Gly216 to Asn223 show no significant continuous electron density in the final Fourier map. This indicates statistical or thermal disorder of these chain segments in trypsinogen in contrast to active trypsin, where they are fixed and form an interdigitating structural unit (“activation domain”). It is remarkable that five of the seven sites where the trypsinogen chain becomes flexible contain glycine residues. These glycine residues are conserved in vertebrate serine proteases. The conformation of the remaining protein segments in trypsinogen is quite similar to trypsin (Bode & Schwager, 1975 a ) . The mean displacement of all fixed main-chain atoms is 0·22 A. The only residue that is completely differently placed, but still immobilized, is Asp194. Its side-chain is rotated about 170° and binds to HiAfter the correct placement of the trypsinogen molecules within the trigonal trypsinogen crystals (Bode et al. , 1976 a ) , the trypsinogen structure has been refined by a constrained crystallographic refinement at 1·8 A resolution. The final R -value is 0·225. The N-terminus, including residues Val 10 to Gly 18, is mobile and projects into solution. Three chain segments forming the specificity pocket in active trypsin and consisting of residues Gly142 to Pro152, GlyA184 to Gly193 and Gly216 to Asn223 show no significant continuous electron density in the final Fourier map. This indicates statistical or thermal disorder of these chain segments in trypsinogen in contrast to active trypsin, where they are fixed and form an interdigitating structural unit (“activation domain”). It is remarkable that five of the seven sites where the trypsinogen chain becomes flexible contain glycine residues. These glycine residues are conserved in vertebrate serine proteases. The conformation of the remaining protein segments in trypsinogen is quite similar to trypsin (Bode & Schwager, 1975 a ) . The mean displacement of all fixed main-chain atoms is 0·22 A. The only residue that is completely differently placed, but still immobilized, is Asp194. Its side-chain is rotated about 170° and binds to His40 in a manner similar to that described for chymotrypsinogen (Freer et al. , 1970). The residues that form the charge relay system in active trypsin have almost identical conformations in trypsinogen. The Ser195 O γ −His57 e 2 pair is slightly different but seems, as in free trypsin, unfavourable for formation of a good hydrogen bond.0 in a manner similar to that described for chymotrypsinogen (Freer et al. , 1970) . The residues that form the charge relay system in active trypsin have almost identical conformations in trypsinogen. The Ser195 O γ −His57 e 2 pair is slightly different but seems, as in free trypsin, unfavourable for formation of a good hydrogen bond.0 in a manner similar to that described for chymotrypsinogen (Freer et al. , 1970) . The residues that form the charge relay system in active trypsin have almost identical conformations in trypsinogen. The Ser195 O γ −His57 e 2 pair is slightly different but seems, as in free trypsin, unfavourable for formation of a good hydrogen bond.0 in a manner similar to that described for chymotrypsinogen (Freer et al. , 1970) . The residues that form the charge relay system in active trypsin have almost identical conformations in trypsinogen. The Ser195 O γ −His57 e 2 pair is slightly different but seems, as in free trypsin, unfavourable for formation of a good hydrogen bond. In general, the activation from bovine trypsinogen to the active trypsin can be described as a transition from a partially disordered zymogen structure with an incomplete substrate contact site to the completely fixed enzyme structure.