This report describes the use of surface plasmon spectroscopy to
study the effect of surface wettability
on the nonspecific adsorption of proteins and detergents to
self-assembled monolayers (SAMs) of alkanethiolates
on gold. The adsorption of both proteins and detergents to
uncharged SAMs showed a general dependence on
the wettability of the surface as determined by the contact angle of
water on the SAM under cyclooctane (θco).
The effect of the wettability of the SAMs on the adsorption of
sodium dodecyl sulfate (SDS) was dependent
on whether micelles were present. Above the critical micelle
concentration (cmc), SDS adsorbed only on
surfaces that gave contact angles with values of cos θco
< 0 (i.e., the transfer of the surface from water to
cyclooctane has a favorable free energy). Below the cmc, the
requirement for adsorption was much more
stringent: SDS adsorbed only on the surfaces that gave values of cos
θco < −0.9. Similarly, the effect of
the
wettability of the SAMs on the adsorption of proteins showed a
dependence on the size of the proteins. The
smaller proteins tested (ribonuclease A and lysozyme) adsorbed only on
the least wettable surfaces tested (cos
θco < −0.83). The larger proteins tested
(pyruvate kinase, fibrinogen, and γ-globulin) also adsorbed best
to
the least wettable surfaces, but adsorbed to some extent on almost all
the surfaces; the single exception was
a SAM presenting hexa(ethylene glycol) groups at the surface, to which
no protein adsorbed. Films of adsorbed
proteins were desorbed from the SAMs by treatment with
detergent.
This paper reports the generation of a self-assembled monolayer (SAM) that selectively binds proteins whose primary sequence terminates with a His-tag: a stretch of six histidines commonly incorporated in recombinant proteins to simplify purification. The SAM was prepared by the adsorption onto a gold surface of a mixture of two alkanethiols: one thiol that terminated with a nitrilotriacetic acid (NTA) group, a group that forms a tetravalent chelate with Ni(II), and a second thiol that terminated with a tri(ethylene glycol) group, a group that resists protein adsorption. His-tagged proteins bound to the SAM by interaction of the histidines with the two vacant sites on Ni(II) ions chelated to the surface NTA groups. Studies with model proteins showed the binding was specific for His-tagged proteins and required the presence of Ni(II) on the surface. Immobilized His-tagged proteins were kinetically stable in buffered saline at pH 7.2 but could be desorbed by treatment with 200 mM imidazole. Surface plasmon resonance studies for two model systems showed that His-tagged proteins adsorbed on the NTA-SAM retained a greater ability to participate in binding interactions with proteins in solution than protein immobilized in a thin dextran gel layer by covalent coupling.
During the SARS-CoV-2 pandemic, novel and traditional vaccine strategies have been deployed globally. We investigated whether antibodies stimulated by mRNA vaccination (BNT162b2), including 3
rd
dose boosting, differ from those generated by infection or adenoviral (ChAdOx1-S and Gam-COVID-Vac) or inactivated viral (BBIBP-CorV) vaccines. We analyzed human lymph nodes after infection or mRNA vaccination for correlates of serological differences. Antibody breadth against viral variants is less after infection compared to all vaccines evaluated, but improves over several months. Viral variant infection elicits variant-specific antibodies, but prior mRNA vaccination imprints serological responses toward Wuhan-Hu-1 rather than variant antigens. In contrast to disrupted germinal centers (GCs) in lymph nodes during infection, mRNA vaccination stimulates robust GCs containing vaccine mRNA and spike antigen up to 8 weeks post-vaccination in some cases. SARS-CoV-2 antibody specificity, breadth and maturation are affected by imprinting from exposure history, and distinct histological and antigenic contexts in infection compared to vaccination.
An ELISA assay is described for measuring the binding of influenza
virus A-X31 to α-sialoside groups
that are linked to biotin-labeled polyacrylamides. The efficacy of
these polymers in inhibiting the adhesion of influenza
virus to erythrocytes (as measured by a hemagglutination assay) was
shown to be directly related to the binding
affinity of the polymers for the viral surface: the differences in
inhibitory efficacy among the polymeric inhibitors
and monomeric α-methyl sialoside, among fractions of a polymeric,
polyvalent inhibitor with narrow molecular
weight ranges, and among polymeric inhibitors prepared by
copolymerization or modification of a preformed polymer
chain, all correlated with differences in the affinity of the
inhibitors for the surface of the virus. The
polymeric
inhibitors studied had affinities for the viral surface that ranged
between 103 and >106 greater than α-methyl
sialoside,
on the basis of total sialic acid groups in solution. The role of
steric stabilization in the mechanism by which these
polymers inhibit hemagglutination was investigated. The ability of
the polymeric, polyvalent inhibitors to inhibit
the binding of a polyclonal antibody to the viral surface suggests that
steric stabilization may also be an important
effect in this system.
In yeast strains bearing the point mutation called GAL11P (for potentiator), certain GAL4 derivatives lacking any classical activating region work as strong activators. The P mutation confers upon GAL11, a component of the RNA polymerase II holoenzyme, the ability to interact with a portion of the dimerization region of GAL4. The region of GAL11 affected by the P mutation is evidently functionally inert in ordinary cells, suggesting that this mutation is of no functional significance beyond creating an artificial target for the GAL4 dimerization fragment. From these observations and further analyses of GAL11, we propose that a single activator-holoenzyme contact can trigger gene activation simply by recruiting the latter to DNA.
This paper describes the use of surface plasmon
resonance (SPR) spectroscopy to measure the rates and
extents of association of four detergentssodium dodecyl sulfate
(SDS), β-octyl glucoside, Triton X-100,
and Tween 20to self-assembled monolayers (SAMs) of alkanethiolates
on gold. SAMs presenting
hexaethylene glycol groups resisted the adsorption of all four
detergents. These same detergents associated
with hydrophobic SAMs presenting methyl groups; the concentration of
detergent molecules on the surface
was 120−280 pmol/cm2. The associations of the
detergents with the hydrophobic SAM were described well
by the Langmuir adsorption isotherm. The dissociation constants
K
d (M) for the desorption of the
detergents
from the surface correlated with the critical micelle concentration
(cmc, M) of the detergents in solution,
and followed the relationship cmc ≈ 7
(±2)K
d. The efficacy of SDS in
removing the protein fibrinogen
adsorbed on a hydrophobic SAM depended strongly on the concentration of
detergent. SDS at a concentration
three times greater than the cmc removed (or displaced) the adsorbed
layer of protein in seconds; SDS at
a concentration three times smaller than the cmc did not desorb it even
after several minutes. This paper
shows that SPR is a useful analytical technique for characterizing the
interactions of detergentsand
other molecules having low molecular weightwith the well-defined
surfaces of SAMs.
We report a method based on mass spectrometry for the characterization of noncovalent complexes of proteins with mixtures of ligands; this method is relevant to the study of drug leads and may be useful in screening libraries for tight-binding compounds. It is based on the ability of electrospray ionization (ESI)* 1•2 3to generate ions of intact noncovalent complexes in the gas phase3-5 and of Fourier transform ion cyclotron resonance
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