Identification of type 1 and type 2 light-harvesting chlorophyll a/b-binding proteins using monospecific antibodies

The amino acid sequences of more than 40 apoproteins of the light-harvesting complex associated with Photosystem II (LHC II) of various plants have been deduced by sequencing their corresponding genes. These highly conserved sequences fall into two major categories, type 1 and type 2, that differ mainly in a small number of domains close to the N-terminus. We have made polyclonal, monospecific antibodies against synthetic peptides corresponding to the most unique sequence domains of the N-terminal regions of type 1 and type 2 LHC II apoproteins, using sequences derived from petunia genes. On Western blots our anti-type 1 and 2 antibodies crossreact with light-harvesting proteins of petunia, tomato, spinach and several other plants. By using a new gel-system based on ammediol (2-amino-2-methyl-1,3-propanediol), we are able to resolve up to eight LHC II apoproteins. On petunia, tomato and spinach blots the anti type 1 antibodies bind to two or more of the higher molecular weight LHC II polypeptides, whereas the anti type 2 antibodies recognize very specifically only one or two of the lower molecular weight LHC-proteins. In all plants studied, the type 1 LHC II apoproteins are more numerous and span a greater size range than the type 2 apoproteins. This is consistent with the smaller number of type 2 LHC II CAB genes that have been discovered to date.