Effective interresidue contact energies for proteins in solutions are estimated from the number of residue-residue contacts observed in crystal structures of globular proteins(http：//www．rcsb．org/) by means of the Miyazawa-Jemiganm (MJ) interaction matrix．It is found that residues can be classified into three groups according tothe contact energles：hydrophobic residues (H)

neutral residues (N)

and hydrophilic residues (P) Here we develop a modified HP lattice model

i．e．a HNP lattice model．In this model

the contact Hanfiltonian is simply written asH=-∑iEsi-sjδ(rij

l)(Si=H

or N

or P) (4)Where EH-R=-5 59RT

EH-N=-3.68RT

EEH-P=-3.07RT

EN-N=-2.23RT

EN-P=-1.78RT

EN-P=一1.37RT

and rij is the distance between residues i and j. We first calculate the conformational properties of the native states of shon Drotein chains using 2-dimensional HNP lattice model and enumeration calculation method The distributions of various types of residue-residue contacts and three types of residues of the native states are discussed We also investigate the folding of the protein with a sequence of HHNHNPNHPPHPNPPHPHPPHHPHNH using the modified HP lattice model Here the sequence is selected at random The folded conformation is obtained in square lattice

and the folding energy is -64.89RT．Our calculation shows that the HNP lattice model may be more reasonable for simulation of the folding behavior of real proteins.