Spectroscopy and microscopy studies of the recognition of amino acids and aggregation of proteins by Zn(II) complex of lower rim naphthylidene conjugate of calix[4]arene.
A lower rim naphthylidene conjugate of calix[4]arene [L] has been synthesized and characterized, and the structure has been established on the basis of single crystal XRD. The L has been found to be selective toward Zn(2+), which induces appropriate changes in the arms of L so that the N(2)O(2) coordination results in the formation of a tetrahedral complex; namely, [ZnL]. [ZnL] recognizes Asp, Cys, His, and Glu from among the naturally occurring amino acids owing to the protonation and chelating ability of the amino acid and the pi-pi interaction ability of the side chain of the amino acid with [ZnL]. All of these features have been demonstrated on the basis of fluorescence, absorption, and lifetime measurements. The rechelation of Zn(2+) by the amino acid used in the titration has been demonstrated on the basis of ESI-MS studies in the case of Cys to result in a Zn(2+) complex having either 5- or 6-coordination. [ZnL] has also been shown to be selective toward glutathione and glutathione oxidized. The amino acids present in the proteins also interact with [ZnL], resulting in dechelation of [ZnL] as well as aggregation of the protein, as demonstrated on the basis of absorption and fluorescence spectroscopy and atomic force microscopy. The alpha-helical proteins (namely, albumins) exhibit greater conformational changes, as compared to the beta-sheet proteins (namely, lectins), as studied on the basis of CD spectroscopy. The aggregation of the proteins when treated with [ZnL] follows a trend: peanut agglutinin < bovine serum albumin < jacalin < human serum albumin. The present studies clearly demonstrated the recognition features of [ZnL] toward Asp, Cys, His, and Glu, and the peptides and proteins containing these by spectroscopy and microscopy studies.
Chinta
Jugun Prakash
JP
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India.
Acharya
Amitabha
A
Kumar
Amit
A
Rao
Chebrolu P
CP
D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D047250:Calixarenes / Q000737:chemistry*; D002417:Cattle; D008853:Microscopy / Q000379:methods; D018625:Microscopy, Atomic Force / Q000379:methods; D009281:Naphthalenes / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry; D010636:Phenols / Q000737:chemistry*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry; D012709:Serum Albumin / Q000737:chemistry; D013050:Spectrometry, Fluorescence / Q000379:methods; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D015032:Zinc / Q000737:chemistry*
D000596:Amino Acids; D009281:Naphthalenes; D010455:Peptides; D010636:Phenols; D011506:Proteins; D012709:Serum Albumin; C121325:calix(4)arene; D047250:Calixarenes; D015032:Zinc