Avoiding nonspecific interactions in studies of the plasma proteome: practical solutions to prevention of nonspecific interactions for label-free detection of low-abundance plasma proteins

The molecular constitution of blood can be highly representative of the physiological state of an individual and offers an ideal target for studies of biomarkers. High-abundance plasma proteins, particularly albumin, dominate the plasma proteome, but it is the low-abundance proteins (such as cytokines) that are commonly associated with many pathophysiological states. Several detection strategies, and particularly those that involve label-free detection, are available for low-abundance protein detection in plasma, but all can be severely compromised by the high-abundance of serum albumin. In the present study, we examine the effect of albumin interference on accurate label-free detection by protein microarrays. Albumin was found to disrupt specific antigen-antibody binding interactions of low-abundance proteins. In clinical analysis, where it is imperative to preserve the integrity of samples, depletion of albumin may further undermine quantitative measurements. We have optimized procedures that permit accurate analysis to be undertaken without the need for prior treatment of samples. The emphasis is placed on disrupting nonspecific interactions including both electrostatic (i.e., Colulombic) and electrodynamic (hydrophobic and other nonpolar based) interactions. These protocols appear to be generic with potential applications in several areas of analytical biotechnology.

Quantitative studies of the interactions of metalloproteins with gold nanoparticles: identification of dominant properties of the protein that underlies the spectral changes

The interaction of cytochrome C and a number of its components such as the apo protein, heme and a coordinated iron with gold nanospheres, has been investigated. The role of the heme group and its effect on the observed spectroscopic properties following binding of cytochrome C to the gold surface has been evaluated. Binding of the heme group directly to the gold is not observed, but the presence of the heme group and its effect on the interaction with the metal surface is shown to be influential. Other factors such as the metal oxidation state and the metal-free heme are also studied. A comparison to serum albumin binding as a nonmetallic protein provides further insight into the interaction characteristics.

Systems biology coupled with label-free high-throughput detection as a novel approach for diagnosis of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a treatable and preventable disease state, characterised by progressive airflow limitation that is not fully reversible. Although COPD is primarily a disease of the lungs there is now an appreciation that many of the manifestations of disease are outside the lung, leading to the notion that COPD is a systemic disease. Currently, diagnosis of COPD relies on largely descriptive measures to enable classification, such as symptoms and lung function. Here the limitations of existing diagnostic strategies of COPD are discussed and systems biology approaches to diagnosis that build upon current molecular knowledge of the disease are described. These approaches rely on new 'label-free' sensing technologies, such as high-throughput surface plasmon resonance (SPR), that we also describe.

Studying protein binding to conjugated gold nanospheres; application of Mie light scattering to reaction kinetics

The study of protein interactions is an area of much interest, particularly towards obtaining more detailed information about biological processes. Current methods involve the use of complicated, specialised techniques which are beyond the scope of most laboratories. Here, we show how information about the binding of proteins to conjugated gold nanospheres can be obtained using straightforward experimental techniques. A Perkin Elmer LS 55 luminescence spectrometer was used to observe the changes in light scattering caused by the binding of complementary proteins to conjugated nanoparticles, measured by the intensity change over time. Mie theory simulations have been used to predict the expected observations and to quantify the changes in intensity as a function of surface coverage. Further kinetic studies have been carried out at 530 nm to obtain more detailed information about the processes involved in the binding reaction. Thus, we have demonstrated that the interaction of proteins can be studied using a straightforward method which provides information about surface coverage and reaction kinetics.