There is a poor correlation between the concentration of an mRNA within a cell and the abundance of the corresponding protein.

The amount of the protein must therefore be measured directly.

There may be a million or more protein molecules per cell if splice variants and posttranslationally-modified molecules are included.

Identification of the protein(s) specifically associated with a disease is therefore a daunting problem.

Using technologies already developed for polynucleotide microarrays are being exploited to create protein microarrays or protein chips.

Worldwide market for protein microarrays expected to grow from $45 million in 200 to $500 million in 2006.

Technology for protein chips involves more steps and more complex science, however.
 

Steps in construction of protein microarray:
 

• choose a surface chemistry that allows immobilized proteins to retain their secondary and tertiary structures and hence biological activity.

• apply an agent to capture proteins of interest

                        antibodies - low specificity but large libraries are available

                        aptamers - protein-binding nucleic acids

                        fibronectins - antibody mimics

                        phage display peptides - protein-binding peptides

• develop a method to determine the degree of protein binding

                        ELISA - based assays using fluorescence or chemiluminescence: sensitive but require protein labelling

                        laser - induced evaporation followed by  by mass spectrometric quantitation: SELDI - TOF: low throughput

                        surface plasmon resonance - mass of bound molecules monitored by light reflection: low throughput, no labelling
 

Potential applications of protein microarrays:
 

• profiling of disease - related proteins

• study of protein - protein interactions

• study of protein - drug interactions

• study of  protein- DNA interactions

• study of protein - lipid interactions

• monitoring enzyme reactions
  

Reviews:

Protein Arrays Resource page - European Science Foundation

Protein microarray Technology - MacBeath lab at Harvard

Hall DA et al. (2006) Protein Microarray Technology. Mech Ageing Dev. Epub Nov 26

Kricka LJ et al. (2006) Current Perpectives in protein array technology Ann. Clin. Biochem. 43:457-467.

P.M. Mitchell (2002) A perspective on protein microarrays. Nature Biotech 20, 225 - 229.

Global analysis of yeast proteome: Heng Z. et al. Science 293, 2101 - 2105.