Equilibrium unfolding of kinetically stable serine protease milin: the presence of various active and inactive dimeric intermediates

Development of a method for the efficient release of N-glycans from glycoproteins generating native deglycosylated proteins

In many cases, it is desirable to maintain the native status of the target glycoproteins when they are deglycosylated. However, most conventional deglycosylation process often causes the irreversible denaturation of the target glycoproteins. In the present study, we developed a deglycosylation method that could obtain the native deglycosylated proteins employing Png1p-ΔH1, which was confirmed to tolerate high concentration of dithiothreitol (DTT). To prove this process, ribonuclease B (RNase B) and Yeast carboxypeptidase (CPY) were employed as the targeting glycoproteins. Our results confirmed that both of them could be completely deglycosylated in the presence of high concentration DTT and could be refolded when DTT was removed. The circular dichroism spectroscopy (CD) measurement of refolded CPY and RNase B indicated that the structure of deglycosylated proteins had recovered their native status. This method offers the possibility of efficiently releasing N-linked glycans from glycoproteins and obtaining the native target proteins.

Metastability of papain and the molecular mechanism for its sequential acid-denaturation

Acid unfolding of non-inhibited papain at pH 2 was studied by means of spectroscopic and electrophoresis techniques as well as activity assays. We found a molten globule like species (A state) similar to that previously reported for bromelain and S-carboxy-methyl-papain. We demonstrated that this A state is not thermodynamically stable but a metastable conformer which decays into an unfolded conformation in a few hours. The mechanism of acid unfolding to the A state proved to be completely irreversible, with a biphasic time evolution of spectroscopic signals characteristic of the existence of a kinetic intermediate. This latter species showed properties in-between native and A state such as secondary structure, exposition of hydrophobic area and tryptophan environment, but a native like hydrodynamic radius. Native papain seems to unfold at acid pH through at least two kinetic barriers, being its pro-region mandatory to conduct and stabilize its active structure. Computer simulations of acid unfolding, followed by ANS docking, identified three regions of cavity formation induced by acid media which might be used as regions to be fortified by protein engineering in the quest for extreme-resistant proteases or as hot-spots for protease inactivation.