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Effects of Hydration on Structure and Phase Behavior of Pig Gastric Mucin Elucidated by SAXS
Malmö University, Faculty of Health and Society (HS), Department of Biomedical Science (BMV). Malmö University, Biofilms Research Center for Biointerfaces.
Malmö University, Faculty of Health and Society (HS), Department of Biomedical Science (BMV). Malmö University, Biofilms Research Center for Biointerfaces.
Malmö University, Faculty of Health and Society (HS), Department of Biomedical Science (BMV). Malmö University, Biofilms Research Center for Biointerfaces.
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2018 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 122, no 30, p. 7539-7546Article in journal (Refereed) Published
Abstract [en]

In this work small-angle X-ray scattering (SAXS) was used to study hydration and temperature-induced changes of pig gastric mucin (PGM) within the entire concentration range. The scattering is interpreted as originating from PGM fiber-like structures that adopt rod-like bottle-brush conformation in dilute solutions. On the basis of the knowledge about molecular structure of mucins and SAXS data for dilute solutions, we propose a theoretical model for predicting mucin conformation in solution and calculate the corresponding scattering profile. This bottle-brush model comprises a protein backbone with carbohydrate side chains and corresponding structural parameters, such as grafting distance and lengths of the backbone and side chains. It describes the experimental PGM data from dilute solutions in the full q range very well. It furthermore suggests that the carbohydrate side chains are grafted with a regular separation of around 5 nm and a length of 14 nm. The cross-section size with a radius of about 1 nm is also in accordance with the size of the carbohydrate units. Structuring of PGM solutions at higher concentrations was investigated by analyzing semidilute and concentrated PGM samples. Starting at about 20 wt %, Bragg peaks become clearly visible indicating a more ordered mucin system. In very dehydrated and fully dry mucin samples these peaks are not present indicating lack of long-range order. The SAXS data show that the structural change occurring at about 80 wt % mucin and 25 degrees C corresponds to a glass transition in agreement with our previous calorimetric results. Temperature also has an effect on the phase behavior of mucin. At intermediate levels of hydration, a phase transition is observed at about 60-70 degrees C. The main Bragg peak appears to split in two, indicating formation of a different structure at elevated temperatures. These findings are used to improve the PGM water phase diagram.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018. Vol. 122, no 30, p. 7539-7546
Keywords [en]
Chemistry, Physical
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:mau:diva-5260DOI: 10.1021/acs.jpcb.8b05496ISI: 000440956300009PubMedID: 29989815Scopus ID: 2-s2.0-85049844913Local ID: 26637OAI: oai:DiVA.org:mau-5260DiVA, id: diva2:1402114
Available from: 2020-02-28 Created: 2020-02-28 Last updated: 2024-02-05Bibliographically approved
In thesis
1. Effect of hydration on thermodynamic, rheological and structural properties of mucin
Open this publication in new window or tab >>Effect of hydration on thermodynamic, rheological and structural properties of mucin
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mucus, an adherent hydrated layer covering the epithelium, is found in all internal tracts of the body and plays an important role in animal and human life. One of the essential functions of mucus is protection of tissues against dehydration. A major component of mucus, forming the macromolecular matrix and also being responsible for its viscoelastic properties, is the glycoprotein mucin. Mucin is a complex molecule owing to the high molar mass, its polydispersity and high degree of glycosylation. This thesis is aimed to investigate how thermodynamic, structural and rheological properties of mucin are affected by hydration. The effect of hydration on thermodynamic properties of pig gastric mucin (PGM) and bovine submaxillary mucin (BSM) has been studied using sorption calorimetry and differential scanning calorimetry (DSC). The analysis of sorption isotherms shows higher water sorption capacity of PGM compared to BSM at relative humidity (RH) levels lower than about 78%. The value of the hydration enthalpy at zero water content at 25ºC for both biopolymers is close to -20 kJ/ mol. RH levels at which glass transition of both mucins occurs are shown to be between 60 and 70%. The RH at which glass transition occurs is weakly dependent on the temperature and mucin type. The phase diagram of PGM demonstrates two different glass transition regions: dependent and independent on hydration levels, respectively. In particular at mucin concentrations from 0 to 67 wt%, the glass transition occurs at a constant temperature of about –15ºC. At higher concentrations of mucin, the glass transition temperature (Tg) increases with increasing mucin concentrations. It is also demonstrated that the QCM-D technique can be used to obtain the water sorption isotherms of mucin films in particular and in general to monitor glass transitions in biopolymers. Hydration-induced changes of rheological properties of mucin films are investigated using a model-free approach. The ratio of G’/G’’ is evaluated as a function of relative humidity. Observed transitions from solid-like behaviour to liquid-like behaviour in mucin system occur in the same humidity range as that found in sorption calorimetric experiments. The structural properties of mucin have been studied using atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS). AFM indicates the presence of dumbbell as well as fiber-like structures in PGM samples. In the case of BSM samples, only fiber-like structures are observed. SAXS studies show three ranges of scattering vector q corresponding to different fractal dimensions in dilute PGM and BSM solutions. Dehydration-induced structural changes in PGM are demonstrated by a distinct appearance of peaks on scattering curves starting from 20 wt% of mucin. Structural changes at about 80 wt% obtained in SAXS at 25°C, correspond to mucin glass transition, and are in agreement with sorption calorimetry and DSC studies. Temperature-induced phase behaviour changes occur around 60-70°C at intermediate levels of hydration. A comparison between water sorption isotherms of BSM/chitosan multilayers and those of individual biopolymers shows that the water sorption capacity of BSM/chitosan multilayers is similar compared to that of individual biopolymers, although some differences exist. In particular, at low RH levels the water sorption capacity of multilayers is slightly higher compared to each biopolymer, however at high RH the multilayer films are less hydrated than individual biopolymers.

Place, publisher, year, edition, pages
Malmö University, Faculty of Health and Society, 2013. p. 69
Series
Malmö University Health and Society Dissertations, ISSN 1653-5383 ; 2
Keywords
mucous gel, mucus, mucin, PGM, BSM, BSM/chitosan multilayers, hydration, water sorption isotherm, relative humidity, water activity, bound water, enthalpy of hydration of biopolymer, glass transition, rheology, phase diagram, fiber-like structure, dumbbell-like structure, sorption calorimetry, DSC, QCM-D, SAXS, AFM
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:mau:diva-7330 (URN)15514 (Local ID)978-91-7104-513-3 (ISBN)978-91-7104-514-0 (ISBN)15514 (Archive number)15514 (OAI)
Note

Note: the papers are not included in the fulltext online.

Paper IV published in dissertation as manuscript with title "Effects of Dehydration on Structural Properties and Phase Behaviour of Pig Gastric Mucin Evaluated by SAXS"

Available from: 2020-02-28 Created: 2020-02-28 Last updated: 2024-03-07Bibliographically approved

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Falk, Yana ZnamenskayaEngblom, JohanArnebrant, ThomasKocherbitov, Vitaly

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Falk, Yana ZnamenskayaEngblom, JohanArnebrant, ThomasKocherbitov, Vitaly
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Journal of Physical Chemistry B
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