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Pollutant-induced modulation in conformation and β-lactamase activity of human serum albumin.

Ahmad E, Rabbani G, Zaidi N, Ahmad B, Khan RH - PLoS ONE (2012)

Bottom Line: These findings were compared to HSA-hydrolase activity.We found that though HSA is a monomeric protein, it shows heterotropic allostericity for β-lactamase activity in the presence of pollutants, which act as K- and V-type non-essential activators.We also show a correlation with non-microbial drug resistance as HSA is capable of self-hydrolysis of β-lactam drugs, which is further potentiated by pollutants due to conformational changes in HSA.

View Article: PubMed Central - PubMed

Affiliation: Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh, India.

ABSTRACT
Structural changes in human serum albumin (HSA) induced by the pollutants 1-naphthol, 2-naphthol and 8-quinolinol were analyzed by circular dichroism, fluorescence spectroscopy and dynamic light scattering. The alteration in protein conformational stability was determined by helical content induction (from 55 to 75%) upon protein-pollutant interactions. Domain plasticity is responsible for the temperature-mediated unfolding of HSA. These findings were compared to HSA-hydrolase activity. We found that though HSA is a monomeric protein, it shows heterotropic allostericity for β-lactamase activity in the presence of pollutants, which act as K- and V-type non-essential activators. Pollutants cause conformational changes and catalytic modifications of the protein (increase in β-lactamase activity from 100 to 200%). HSA-pollutant interactions mediate other protein-ligand interactions, such as HSA-nitrocefin. Therefore, this protein can exist in different conformations with different catalytic properties depending on activator binding. This is the first report to demonstrate the catalytic allostericity of HSA through a mechanistic approach. We also show a correlation with non-microbial drug resistance as HSA is capable of self-hydrolysis of β-lactam drugs, which is further potentiated by pollutants due to conformational changes in HSA.

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Difference in sequential unfolding of albumin (N) in absence and presence of pollutants.At mild temperature domain I and II separates and domain III melts out giving an expanded (E) conformation to the albumin. iDII and iDI corresponds to intermediates populated from the melting of domain II and I respectively and U is unfolded albumin.
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pone-0038372-g007: Difference in sequential unfolding of albumin (N) in absence and presence of pollutants.At mild temperature domain I and II separates and domain III melts out giving an expanded (E) conformation to the albumin. iDII and iDI corresponds to intermediates populated from the melting of domain II and I respectively and U is unfolded albumin.

Mentions: The non-bonded interactions between planar aromatic rings are known as π-π interactions. These aromatic rings tend to form high-order clusters of parallel staggered axially symmetric system, which is a potential minimum configuration in the Lennard-Jones-Coulomb empirical potential calculation. The entropy driven π-stacking interactions stabilize the tertiary structure of protein where upon aromatic ring interaction with water molecules from the rings are released and the overall entropy of the thermodynamic system increases. Two aromatic boxes composed of Tyr150, Phe211, Phe223 and Trp214 in Sudlow site 1 and Phe403, Tyr411 and Phe480 in Sudlow site 2 are formed for the pollutants molecules (Figure 2B). The radial distances from the centered pollutants to each of the aromatic rings is between 3.5 and 4.0 Å, obtained from our previous study [9], fulfills the requirements of van der Waals and π–π interactions [26]. This radial distance is the shortest for 2N and this property of the ligand-binding site for 2N probably gives an unusual stability to the tertiary structures of the HSA molecule (Table 4). From the results of thermal denaturation, we found two populations of intermediates at two temperatures. The first temperature-induced intermediate (iDii) was formed before the actual Tm of HSA and the other (iDi) was formed after the Tm values of albumin which is consistent with the previous reports on thermal denaturation of serum albumin where the first intermediate was considered the result of domain II disruption and the second of domain I disruption [27], meaning that thermal unfolding of HSA is a multistep and multistate process which is schematically summarized in Figure 7 and is consistent with the previous reports [27]. In the scheme, the smaller size of HSA complexed with pollutants than its native form as well as the delayed events of domain melting can be seen. Here, the difference in thermodynamic parameters obtained from secondary and tertiary structural probes revealed that thermal denaturation of HSA is not a monomolecular two state process in equilibrium. Taking into consideration equilibrium conditions simplifies our studies and allows us to compare the stability of HSA under the different conditions of various pollutants.


Pollutant-induced modulation in conformation and β-lactamase activity of human serum albumin.

Ahmad E, Rabbani G, Zaidi N, Ahmad B, Khan RH - PLoS ONE (2012)

Difference in sequential unfolding of albumin (N) in absence and presence of pollutants.At mild temperature domain I and II separates and domain III melts out giving an expanded (E) conformation to the albumin. iDII and iDI corresponds to intermediates populated from the melting of domain II and I respectively and U is unfolded albumin.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3369883&req=5

pone-0038372-g007: Difference in sequential unfolding of albumin (N) in absence and presence of pollutants.At mild temperature domain I and II separates and domain III melts out giving an expanded (E) conformation to the albumin. iDII and iDI corresponds to intermediates populated from the melting of domain II and I respectively and U is unfolded albumin.
Mentions: The non-bonded interactions between planar aromatic rings are known as π-π interactions. These aromatic rings tend to form high-order clusters of parallel staggered axially symmetric system, which is a potential minimum configuration in the Lennard-Jones-Coulomb empirical potential calculation. The entropy driven π-stacking interactions stabilize the tertiary structure of protein where upon aromatic ring interaction with water molecules from the rings are released and the overall entropy of the thermodynamic system increases. Two aromatic boxes composed of Tyr150, Phe211, Phe223 and Trp214 in Sudlow site 1 and Phe403, Tyr411 and Phe480 in Sudlow site 2 are formed for the pollutants molecules (Figure 2B). The radial distances from the centered pollutants to each of the aromatic rings is between 3.5 and 4.0 Å, obtained from our previous study [9], fulfills the requirements of van der Waals and π–π interactions [26]. This radial distance is the shortest for 2N and this property of the ligand-binding site for 2N probably gives an unusual stability to the tertiary structures of the HSA molecule (Table 4). From the results of thermal denaturation, we found two populations of intermediates at two temperatures. The first temperature-induced intermediate (iDii) was formed before the actual Tm of HSA and the other (iDi) was formed after the Tm values of albumin which is consistent with the previous reports on thermal denaturation of serum albumin where the first intermediate was considered the result of domain II disruption and the second of domain I disruption [27], meaning that thermal unfolding of HSA is a multistep and multistate process which is schematically summarized in Figure 7 and is consistent with the previous reports [27]. In the scheme, the smaller size of HSA complexed with pollutants than its native form as well as the delayed events of domain melting can be seen. Here, the difference in thermodynamic parameters obtained from secondary and tertiary structural probes revealed that thermal denaturation of HSA is not a monomolecular two state process in equilibrium. Taking into consideration equilibrium conditions simplifies our studies and allows us to compare the stability of HSA under the different conditions of various pollutants.

Bottom Line: These findings were compared to HSA-hydrolase activity.We found that though HSA is a monomeric protein, it shows heterotropic allostericity for β-lactamase activity in the presence of pollutants, which act as K- and V-type non-essential activators.We also show a correlation with non-microbial drug resistance as HSA is capable of self-hydrolysis of β-lactam drugs, which is further potentiated by pollutants due to conformational changes in HSA.

View Article: PubMed Central - PubMed

Affiliation: Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh, India.

ABSTRACT
Structural changes in human serum albumin (HSA) induced by the pollutants 1-naphthol, 2-naphthol and 8-quinolinol were analyzed by circular dichroism, fluorescence spectroscopy and dynamic light scattering. The alteration in protein conformational stability was determined by helical content induction (from 55 to 75%) upon protein-pollutant interactions. Domain plasticity is responsible for the temperature-mediated unfolding of HSA. These findings were compared to HSA-hydrolase activity. We found that though HSA is a monomeric protein, it shows heterotropic allostericity for β-lactamase activity in the presence of pollutants, which act as K- and V-type non-essential activators. Pollutants cause conformational changes and catalytic modifications of the protein (increase in β-lactamase activity from 100 to 200%). HSA-pollutant interactions mediate other protein-ligand interactions, such as HSA-nitrocefin. Therefore, this protein can exist in different conformations with different catalytic properties depending on activator binding. This is the first report to demonstrate the catalytic allostericity of HSA through a mechanistic approach. We also show a correlation with non-microbial drug resistance as HSA is capable of self-hydrolysis of β-lactam drugs, which is further potentiated by pollutants due to conformational changes in HSA.

Show MeSH
Related in: MedlinePlus