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Comparative thermodynamic study of pepsinogen and pepsin structure

1981; Elsevier BV; Volume: 152; Issue: 2 Linguagem: Inglês

10.1016/0022-2836(81)90253-9

1089-8638

Petkr L. Privalov, Pedro L. Mateo, Н. Н. Хечинашвили, V. M. Stepanov, Lyudmila P. Revina,

Protein purification and stability

Pepsinogen, pepsin and its C-terminal fragment have been studied thermodynamically in solution by a scanning microcalorimetric method at various pH and salt content values. It has been shown that: (1) thermal denaturation of pepsinogen is a highly reversible process that takes place within a narrow temperature range depending upon the prevalent conditions, but under no condition does it correspond to a two-state transition. This process can be approximated by two quasi-independent transitions, indicating that the pepsinogen molecule consists of two slightly interacting, co-operative structural blocks of different size. (2) Thermal denaturation of pepsin is a complex process that proceeds in two distinct stages occurring at different temperatures, only the second being completely reversible. These stages correspond to separate meltings of two independent parts of the molecule, these being the N-terminal lobe and the more stable C-terminal lobe. Neither of these stages represents a two-state transition. Analysis of these transitions shows that both parts of the pepsin molecule consist of two quasi-independent, co-operative units. (3) All four co-operative units of pepsin have a compact structure with a welldeveloped hydrophobic core, and therefore these units should be regarded as structural domains of the molecule. Consequently, each lobe of the pepsin molecule represents a structural block consisting of two domains. In the presence of pepstatin, the two domains in the N terminal lobe co-operate to form a single system. (4) In pepsinogen, the above-mentioned blocks are much less independent than the co operative units in pepsin, and it is likely that each of them consists of two merged domains. Therefore, release of the 44-residue N-terminal polypeptide upon activation of pepsinogen leads to a loosening of the domain structure and to an increase of interdomain motility of the molecule.