The analysis of residue-residue contacts in protein structures can shed some light on our understanding of the folding and stability of proteins. In this paper

we study the statistical properties of long-range and short-range residue-residue contacts of 91 globular proteins using CSU software and analyze the importance of long-range contacts in globular protein structure. There are many short-range and long-range contacts in globular proteins

and it is found that the average number of long-range contacts per residue is 5.63 and the percentage of residue-residue contacts which are involved in long-range ones is 59.4%. In more detail

the distribution of long-range contacts in different residue intervals is investigated and it is found that the residues occurring in the interval range of 4-10 residues apart in the sequence contribute more long-range contacts to the stability of globular protein. The number of long-range contacts per residue

which is a measure of ability to form residue-residue contacts

is also calculated for 20 different amino acid residues. It is shown that hydrophobic residues (including Leu

Val

He

Met

Phe

Tyr

Cys and Trp) having a large number of long-range contacts easily form long-range contacts

while the hydrophilic amino acids (including Ala

Gly

Thr

His

Glu

Gln

Asp

Asn

Lys

Ser

Arg

and Pro) form long-range contacts with more difficulty. The relationship between the Fauchere-Pliska hydrophobicity scale (FPH) and the number of short-range and long-range contacts per residue for 20 amino acid residues is also studied. An approximately linear relationship between the Fauchere-Pliska hydrophobicity scale (FPH) and the number of long-range contacts per residue CL

is found and can be expressed as CL = a + b × FPH where a = 5.04 and b = 1.23. These results can help us to understand the role of residue-residue contacts in globular protein structure.